In a strong sense, there is no secret sauce. See: <a href="http://www.paulgraham.com/before.html" rel="nofollow">http://www.paulgraham.com/before.html</a>
It is straightforward, but not easy.<p>You should have at least one of the following, preferably two or all:<p>1. A prototype or minimum viable product with proven market demand, users and strong traction numbers.<p>2. A solid idea backed up by a strong, proven team of founders. For example, MIT or Stanford PhDs with heavy domain experience in AI research. Or a pair of founders who have exited one or two startups before.<p>3. Recommendations from YC partners who will vouch for you and your application.<p>My opinion based on observation is that that list is in order of importance. You will probably not get the third option unless you have one of the other two.
i think there is no secret sauce , if your priority is getting into YC over building a successful business you're most likely doing it wrong. P.S im no way affiliated to YC