When you are first getting to know someone, risky topics are PAST RELATIONSHIPS, religion, politics (they might fall asleep ;) and sex.
These topics can lead to the wrong kind of heated discussions and are sometimes best to avoid, depending on how well things are going. It can be good to have a light and cheery conversation on the first date and get into the dangerous topics on a future meeting when you know each other better.
If you do get into these areas of conversation, either by accident or your date brings them up, try keep a level head and respectfully listen to the opinions of your date. Maybe they might even make you reconsider some of your own ideas. Perhaps these are deal breakers for you and you want to sort them out before wasting your time, but just proceed with caution.
People who constantly bring up a past relationships are probably the biggest problem here. Your new potential partner really doesn't want to hear about your past failures, even if it wasn't your fault. Don't treat your date as a therapy session.
Religion can be very personal and risky to talk about. But if this is something that is a deal breaker, perhaps it is something you want to deal with early on.
Some people have very strong feelings about politics and you might as well. On a first date, this might turn into a passionate discussion of the negative type.
Don't beat up on yourself too much. You are trying to show your positive side and put your best foot forward. A few self deprecating jokes can be fun, but you should not be constantly putting yourself down.
Get Too Far Ahead of Yourself
It is probably best not to start sorting the names out for your future children on the first date. Don't scare your date with too many future plans and enjoy the now.
See for dating conversation starters you should be using to get the initial conversation flowing.