The start is the most important part of the race. Get a good start and you have a good chance of placing well. Get a poor start and you can usually forget about placing in the top third of the fleet. So how do you get a good start? Here are some tricks I've learned.
1) Make sure that your timer is accurate and in synch with the committee's timer. I find it nearly impossible to hit the five minute timer exactly when the committee hits theirs, therefore I let 5 seconds run off my timer (so it is set to 4:55) so that when I hear the horn (see the flag) I can count 1000-1, 1000-2, etc and then hit start. No matter what I'm doing when the horn goes off I can always hit start within 5 seconds...
2) Try to figure out who are the more aggressive racers and watch them closely. Try not to let them force you commit a foul in the prestart, and try to gain as much advantage as you can. Often being out of synch with everyone else's back and forth is helpful, but not always. Every start is different!
3) In consistent wind, at about two minutes, I sail on port tack, beam-ish reach for one minute, then tack back to starboard and head for the line. I figure, one minute out, one minute back...
4) In flukey wind, or very light wind it is usually better to hang closer to the line. Terrible to get caught 10-15 boat lengths away, dead in the water, when the horn goes off...