It is straightforward, but not easy.
You should have at least one of the following, preferably two or all:
1. A prototype or minimum viable product with proven market demand, users and strong traction numbers.
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.
3. Recommendations from YC partners who will vouch for you and your application.
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.
