Interviews are a tricky thing to administer well. I still remember overflowing with nervous energy when I interviewed with Yelp and Google a couple years ago, wondering whether I'd make a complete fool of myself when it came time for the inevitable programming challenge. I stumbled through the various questions, handling some easily and getting completely flustered by others, and overall was relieved when the ordeal was over. Perhaps most importantly, the whole time I had basically zero clue what I was doing or how I should be presenting myself -- I was simply going with the flow and testing out whatever anecdotal advice I picked up along the way.
Having spent a year or so on the other side of the table, there are several easy ways to improve how you come across in an interview -- and none of them involve cramming!