Amazingly enough its the simple things that make me give up on someone right away. Dont dress like a slob, sit up, seem energetic, smile, dont whine. We simply dont want to hear about problems. Sorry but it gets old. Leave most personal stuff out unless asked. Dont avoid answering tough questions, just dont whine about it if it was a negative thing. And remember sometimes folks ask questions just to see how you do under stress and there is no right answer or the answer doesnt really matter. There is just a calm, sometimes funny way to work through the answer and make a guess. Last interview I was asked a basic two trains leave the station math question and I had to laugh out loud. Its been more years than I can imagine since I did anything other than simple math so I gave it a shot but didnt stress about the answer. Got the job so it worked. Good luck.
"Yesterday I was clever and tried to change the world. Today I am wise and try to change myself." -Rumi