Then make sure to work this into your answers, even if the question they ask you seemingly isn't related to it.
I learned this from one of the co-founders of a SwipeGood (YC W11), they wrote about it in much detail here:
http://blog.close.io/tough-interview-questions
(Now of course - do this mindfully, not robotically, but if you've been invited to an interview, I probably don't need to say this).
And congratulations! Wishing you success :)
1] Paul Graham - wrote an Essay - How To prepare for the interview
> http://old.ycombinator.com/howtoprepare.html
2] I created a summarized, annoted version of 'Grahams essays key points' aka my TLDR
> http://sospep.com/view/article?id=4457
I would memorize those keypoints
3] I also compiled a list of the 'interview questions' that they are known to ask?
> http://sospep.com/view/steps?id=129
you/your co founders probably want to know the answer to every 1 of those questions, as they pertain to your company, backward, forwards and sideways :)
4] and a few other resources, that may be helpful to you... - like ARTICLE(s) - our interview with ycombinator by ... (* x) - i will add the links to the Reference section the article i posted above
Finally, congratulations, I suspect the bar to YC is pretty high and you've cleared the first hurdle. Now get started practicing those interview ?'s and good luck!