A few people have asked me for my advice about this. So I figured I'd put it here and refer future people here.

I am not going to claim that I know how to get into YC. I think that I have justified true belief about what kind of founders YC looks for, but justified true belief is not always knowledge¹.

I don't think the application is important. I could be wrong.

I think the best way to get an interview is to network with former YC founders and get referrals.

This is not an unfair hack, and it is actually a test of important skills. For example, can you effectively sell yourself and your business idea? Are you able to get the attention of busy people? If you have these skills, you are likely to get referred by founders, which will almost guarantee you an interview. Again, these are not trivial skills. For example, when you’re hiring, it will be imperative that you can convince intelligent people to believe in you and your mission. For this reason, I view the YC referral pipeline as a test of important skills, not a backdoor that should be frowned upon.

YC is evaluating founders, not ideas. They are not looking for a specific profile, but there are a few things YC does look for in a founder, and they are very open about this.

Being “hacky”. The real world is not optimized and playing systems to your advantage in unorthodox ways is something YC looks for. I suggest you reflect on any shortcuts you’ve taken, times you found a novel way to accomplish something, or got out of something in a creative way. This relates to Paul Graham’s “relentless resourcefulness”. I would strongly suggest reading at least a fee of Paul Graham’s essays if you are interested in YC. Much of what you learn in YC comes from or is reflected in these essays.

Being honest and straightforward. It is highly unnatural, but you should begin with the answer and follow with the explanation. How many customers do you have? “Well, we have several people interested and…” Just say you have 0 customers, then say whatever you were going to say as succinctly as possible. This is small but it will be appreciated.

Know your customer. Think through the different customer profiles, such as consumer vs. business. Divide those into different profiles. I would recommend really getting in the weeds of who your customer is, and speaking to as many as you can before the interview. If you know who your customer is, you will have a hard time explaining why you haven’t had at least several conversations with them already.

Know your market. YC is looking for billion dollar companies. It’s not essential, but I would recommend that you think through how your product or service can get to 1 billion and in which ways the market will evolve. This is of course pointless and impractical because you will likely iterate in new directions, but it shows that you are interested in scale and want to make something big.

Be technical. Not much you can do about this but learn. If you are not technical, I strongly urge you to apply with a technical co-founder.