Twice a year, the prestigious incubator program called Y Combinator (YC) accepts applications for aspiring entrepreneurs. Having completed the program in 2009, and now serving as a Part Time Design Partner, here's my advice to those who wish to apply. You'll want to communicate the following within your answers:

Describe why you and your co-founders are the right team for the job. If you're a close knit unit, say so.
Show explicitly how you're going to make revenue. Maybe you already are (say so) or have good ideas how to. Nothing beats having >$1 revenue going into the application.
Will you pursue your idea even if you don't get accepted into YC? If yes, make it known.

Read up on Paul Graham's essays here, starting with the "18 mistakes that kill startups".

Apply here. Best of luck.