1) Avoid talking about past relationships. Although it seems like a smart thing to do to size someone up, these conversations get awkward after a few minutes and usually ruin dates.

2) Avoid talking badly about other people, because the person you are on a date with will think you will go around talking badly about him/her too as soon as an opportunity occurs.

3) Avoid talking about money. If you have a lot of it, talking about it may make you seem pompous, or if you do not have any, talking about it will make it seem like you want someone to be sympathetic (in a first date you want to avoid sympathy which can come from pity), or the person may think you are a gigolo or gold digger, both of which you want to avoid.

So just go out and be yourself and have fun and avoid talking about these things which you can talking endlessly on your second date.