-Get ready for high highs and low lows, and practice keeping yourself in the middle or you'll never get good work done. You're going to be pretty sure your company is dying at least once a month, and it usually isn't. This is very important and very difficult to learn.
-Focus on the product, especially in the early days. You'll have time to make deals later. Now, you've got to build something great.
-If you hire, do it very slowly and carefully. The culture of a company is set very early, and so is the quality of the team.
-Don't be afraid to change your idea if the market seems bad. Early is a good time to do it. You can change your product, you can change your team, you can change your sales strategy, but you can probably not create a market. Good startups surf someone else's wave.
-Figure out what the important things are, and spend lots time on those and little on the rest. Lots of startups work very hard, but on the wrong things. They still die an untimely death.
-Watch out for fights and brewing tension among cofounders (ie, make sure everyone feels they have a reasonably fair deal). I've seen this derail more early startups than anything else. And, if you are really sure you have the wrong cofounder, fire fast.
-The startups in my Y Combinator 'class' that tanked the fastest were the ones that spent the most time worrying about option grants for members of their board of advisors and the least time on their product. Could be a coincidence, but why risk it? Build your product.
-Great products, technology, and people win the day in the long run. History backs this up. Do not be afraid of competitors without them, no matter how much money they raise or how much noise they make.
-It's most tempting to give up right before you're about to succeed.
Best of luck,
Sam Altman
Few startups build something great and then die. Nearly all startups that fail to build something great die. Therefore succeeding is identical with building something great, plus or minus about 1%. In phase 1, doing anything else except making something great (fussing over paperwork, arguing with one another, working on other projects, worrying about competitors) is a mistake.