And as a disclaimer: these are my opinions and my advice.  They may or may not fit within everyone's experience and if you don't agree or like them, please feel free to seek out information from other's.

• Know How Much You Can Afford: This seems like common sense but even Steve and I had a larger assumption of what we could afford than what we really could.  And the worst downfall of this syndrome is that you could potentially fall in love with a house and not be able to afford it.  And then you want it so bad that you stretch and stretch to get it and end up in a house that you struggle to pay for.  That is what makes homebuying not fun and foreclosure is a nasty, nasty thing.  Which leads me to my next point.
• Stick to Your Price Range: While your realtor should have your best interest at heart (assuming you are working with your OWN realtor instead of dealing with the seller's agent), some may try to talk you into looking at house that are out of your price range - just to look!  And then you fall in love again and well, see above.  We, thankfully, didn't have this problem because our realtor was amazing (aside from the fact that we really picked out the properties we wanted to see and told him to show them to us so it wasn't like he was picking properties for us) but it's just something to be aware of.
• Get Pre-Approved: When you are really ready to buy a house and have shopped around the banks and lenders for the best rates and incentives, it is a good idea to get a pre-approval letter to have in hand.  These typically last around 60 days or so and will make the seller and their agent realize that you are serious about the offer and may give you a leg up on someone else making an offer who doesn't have a pre-approval.  And note: there is a difference between pre-qualification and pre-approval.  Pre-qualification is based solely on information you have provided to the lender without them checking your credit.  Therefore, once they check your credit and your income, the amount could vary drastically.  Pre-approval, on the other hand, means they've already run all your credit and financials and are willing to offer you that particular amount based on that information and it shouldn't vary much, if at all.
• Know the Industry and the Terms: You don't have to be real estate genius, but like any major financial decision, it is in your best interest to be well informed of what's happening.  This could mean anything from reading articles on the state of the market (especially important in today's market), checking interest rates or looking up every term your realtor or lender throws at you that you don't know.  Use your resources wisely.  Ask questions when you don't know what's going on.  Don't just assume that everyone else has your best interests at heart because it's a money-making venture and you can be taken for a ride.  Ask them to clarify how things work if you don't know and ask over and over until you understand.  Remember, it's nobody's fault but your own if you don't care enough to teach yourself.
• Read and Understand What You're Signing:  This is common knowledge and really should be followed across all walks of life.  Never put pen to paper unless you have read and understood everything because there could be some clause in there you might miss and ignorance is no excuse when the ink has dried.  However, take this advice and combine it with above.  If you read something and don't understand what it means, ask.  Or look it up if it's a definition.  Our realtor actually sat down with us for an hour and half and pretty much explained, line by line, what the sales contract stated and what we were offering the seller and asking for.  If you aren't that lucky, than make sure you are looking out for yourself.
• Know Your Loan Programs:  It would be very beneficial for you to understand the different loan programs available.  I had an advantage on this because not only did I work very closely with the mortgage department learning the process inside and out but my mother has been a loan processor/underwriter/closer most of her life.  However, there are tons of resources available that will explain the advantages and disadvantages of each program.  My general consensus that I have learned over the years is that a conventional fixed-rate mortgage is probably the best, especially for first-time homebuyers who plan to stay in their home for awhile.  Stay away from Adjustable Rates and Interest Only's because those are really designed to get you into a house that you can only afford RIGHT NOW.  Down the line, the payments will change and they may change drastically.  If you can't afford a fixed-rate loan then you probably can't afford to buy your home yet.
• Check Out Downpayment Assistance Programs: I will tell you that Steve and I are doing 100% financing, which technically isn't the smartest.  However, since we are doing a conventional fixed rate mortgage and are not required to carry PMI (look it up if you want to know - you need the practice!! LOL), it's a little less risky for me.  But, there are downpayment assistance programs available all across the nation and they usually take the form of grants or loans, in the basic sense.  We checked them out for ourself and because our combined income was fairly high, the "downpayment assistance" for us would be a loan that kicked in after three years in the house with an interest rate hovering over 10%.  For us, this wasn't feasible - adding another loan payment.  So wrapping it into the mortgage was a better solution.  However, if your income is lower, you may qualify for one you don't have to pay back so it definitely doesn't hurt to do some research.
• Do Legwork on Your Own:  Just because you have a contract with your realtor to find you a house doesn't mean you should sit back and let him do all the work.  Get out there!  Search the free Internet MLS listings - they're less detailed than what the realtors have access to and are not updated as quickly but if you find something you like, you can send it to the realtor to get more information.  Drive around the neighborhoods - this helps you find the areas you like as well as alert you to homes on the market in the area (this is why they say curb appeal is important).  Yes, your realtor is there to do a job but it's also up to you to play an active role in finding the house you like, especially if finding the "right" place is important. 
• Know When It's Perfect:  There's a fine line in finding the house you like.  A few weeks ago, I would tell you to buy the first thing you fell in love with.  But perhaps that's not always true.  I wouldn't however, advocate that keep looking and looking and looking.  Because at some point, all houses blend into the next and you sometimes forget what you're looking for.  So think of these things:
• Know your dealbreakers:  It's a good idea to make a list of what you absolutely need, what you want and what you absolutely don't want.  And prepare to be flexible.  No house is going to have every single thing and if you keep looking for everything, you'll eventually wind up with nothing.  You need to know what you could potentially do without if the house had everything else you wanted.  And here's a good tip: if you keep looking and looking and find that no house is meeting your standards, then perhaps you aren't ready to buy.
• Understand Potential: I'm not saying that it should be a complete shithole.  What I am saying is that you need to learn to see past the interior design and structure and figure out if it can work for you.  You bring your own style and creativity to a house and just because there's a yellow toilet in an otherwise gorgeous bathroom in a house that has everything else (I know, odd scenario, but you get my point) doesn't mean you should say no.  Because toilets are easily replaced.  Maybe something you didn't want to spend but overall, if it gets you the place you've always dreamed of, are you really going to let a crapper stand in your way?
• Know When to Walk Away: This market is a funny one.  On one hand, it's a buyer's market because it has pretty much bottomed out and there are more people trying to sell than those trying to buy.  However, it can also hurt a potential buyer because there are many, many sellers who have loans for so much more than the house is worth now (due to the housing boom a few years ago) that they may be unable to come down as low as you (or the comps) think is fair.  So here's the deal: know when to walk away.  You may really, really, really want a house but if the seller won't come down to a fair price (and this is where your realtor does his job by showing you and explaining comparables in the neighborhood), it's probably in your best interest to walk away.  Nobody should have to beg for a house in this market.  And you may end up paying much more than the house is appraised for (note: another thing to know though, is that if the appraisal comes back lower than the selling price, you have a right to renegotiate - and you should because the bank could deny your loan) and this will hurt you in the end.  Going into a home owing more than it's worth is a stupid practice, especially when there are so many other choices on the market right now.
• Get A Home Inspection!: I can't stress this enough and this is probably the number one piece of advice you should take with you.  A home inspection needs to be paid out of your pocket and cannot be factored into the loan or closing costs.  Ours ran $350 and it is worth every penny.  The home inspector takes a thorough look over the entirety of the house and tells you if there is anything wrong with it.  He will point out things ranging from needing to be fixed right now to things that will need attention in the future.  And from there, you have the right to ask the seller to repair certain things (usually roof leaks, HVAC, plumbing and electricitiy issues are required to be addressed).  However, you go in with a list of things that you know need to be fixed and ultimately, if it's too much for you to handle, you can walk away from the deal.  I believe anyone who buys a home that was built any later than three years before should have a home inspection simply because it covers your ass.  If you don't have one on an older home, you deserve everything that gets thrown at it (and that's not me being harsh - that's me being real because if you have resources available and you don't use them, you don't have any right to complain!).
• Make Sure Closing Costs are Covered: Be aware of the fact that even if you are financing the home a 100%, you will still need to come to the table with some cash to cover particular fees that get paid up front (document, processing, attorney, etc.).  Usually, it's about 2% - 4% of your purchase price and this is cash you will have to bring to closing.  When applying for a loan, the lender should supply you with a Good Faith Estimate and this should give you not only your estimated monthly payment (minus property taxes, insurance and any HOA or PMI fees) but your estimated closing costs.  Also be aware of the fact that this money needs to be in assets - you cannot borrow from a credit card or a relative.  It has to be cash on hand in a savings or checking account.  We actually asked our seller to pay $3000 of our closing costs which, God willing, should cover them all, so this might be an option to explore as well.  Another note: even when the seller pays the closing costs, the buyer is ultimately paying them - it's just the difference of whether you as the buyer are coming to the table with cash or wrapping it up into your loan (the seller provides the hard cash at that point).
• Plan for Things You'll Need: This is especially true for all you first-timers.  I'm a week away from closing and so much stuff that we need/want keeps running through my head.  So you just need to prioritize.  If you are living in apartment, you're going to need things like lawnmowers and garden hoses and such.  Start to make a list and determine what you will need first.  For instance, you probably need to buy a lawnmower before you get a patio set or a grill because both are going to be awfully useless if your yard looks like crap (even more so if you have an HOA and will be required to keep you lawn in nice condition or face hefty fines).  Me?  I'm buying new furniture! :-)

So for now, that's the best I have.  If you read it, kudos to you and I hope this help.  If you have any more advice to contribute, please leave it in the comments.  Same with questions - leave them in the comments and I'll answer to the best of my limited knowledge.  I'll probably add to this list as we get further into it but if my personal advice helped someone else understand things, than that makes everything right with the world.