The First Meet Up
Notice this article is called the first 'meet up' not the first date. By the time you decide to meet with someone in person, you've generally only exchanged emails and perhaps had a phone conversation or two. Although you might be interested in eachother, the first face to face meet up is really a meet and greet sort of deal. Remember, until you actually meet, you don't have any idea who the person really is, some online daters even go so far as to lie about their gender.
Time and Place
The first meetup should be in a busy public place in broad daylight for obvious safety reasons. The late afternoon is a perfect time, because if you really feel like you've hit it off, it is easy to continue to meet up to a more traditional date atmosphere like a restaraunt for dinner. To protect yourself and your privacy, it is best if you each travel seperately to and from the meet up location.
What To Do
Because neither of you will really know what to expect, its smart to keep the date as low key as possible. Meeting for a cup of coffee is perfect. Anything that is cheap/free, casual, and easy to bail out from is perfect. Also, remember why you are meeting this person; you need to go somewhere that is good for conversation so you can get to know each other. Going to see a movie might sound like fun, but movie theaters are possibly the worst places to get to know someone.
Alcohol can seriously impair your decision making skills and supress your inhibitions. A first meet up is not the time to start tipping back too many drinks.
After your first meet up with a stranger from an online dating site you have a decision to make. Do you want to see them again or not? If you weren't satisfied, there is no reason to contact them again, as any correspondence could be seen as positive. If they contact you first it is fine to politely say no thanks. If, however, you do want to see this person again, you should really take the initiative to contact them. Some etiquette may say to wait a day or two, but any longer than that and they may have moved on. A friendly phone call and a little honesty can go a long way when looking to continue the relationship. Don't fall into the trap of playing too hard to get.