I recently interviewed with Facebook and here are a couple of the questions they asked me:

1) how do you find the square root of a number using only basic operations?

2) how do you position a button over the bottom right corner of an image using only css?

I spent a lot of time reviewing my linked lists and other basic data structures, but that ended up being wasted time. In my case, I knew the answers to both, but let my nervousness ruin my responses. So my biggest advice is to just relax and trust that you'll be able to figure it out. Good luck!