There are a lot of concepts and subtleties that underly a TOS document. However, to get a decent one, all you have to do is pick a big relatively similar Internet site, and copy theirs. Replace their name with yours, and their jurisdictional information with yours (e.g. state names). That's the starting point. Then look at the other big Internet sites, and copy anything you feel is applicable. Then read it slowly. If you don't understand anything, post it here and someone can probably help you understand what it is talking about.
I don't recommend hiring a lawyer. They will either go through basically the same process as described above anyway and then charge you a lot for it. If you have a specific issue with your site, you might want to hire a lawyer to help you draft specific provisions that deal with that issue. But seriously, do you have an issue that facebook/craigslist/ebay/microsoft/amazon/etc. don't?
If you really want to understand what is going on, I suggest reading this book: http://www.amazon.com/Electronic-Commerce-Ronald-J-Mann/dp/0... and the cases and statutes it references. But this is really unnecessary to get something decent.
I don't recommend hiring a lawyer. They will either go through basically the same process as described above anyway and then charge you a lot for it. If you have a specific issue with your site, you might want to hire a lawyer to help you draft specific provisions that deal with that issue. But seriously, do you have an issue that facebook/craigslist/ebay/microsoft/amazon/etc. don't?