Enjoy the short period of exhiliration. Then be prepared to ride the roller coaster of emotions. You will enjoy both highs and lows that top anything in your previous experience. Once you've done it you will learn there is no better job. Best of luck!
Don't overwork yourself. Get at least 7 hours of sleep. Exercise at least 3 times a week. Keep a pulse of your venture and know when to move on if things aren't looking good. Life is short so don't kill yourself with one thing, you must iterate. Make time for family and friends.
These are some of the things I've learned over the years. Please add to this list if you think of anything else.