I've been doing it on and off since 2004. There have been some wins and some losses. Unfortunately, I haven't been as disciplined as maybe I should have been. I do follow some general rules though:
1.) As a Christian I avoid any company that I believe is profiting from sin. For instance, I won't buy into an alcohol company. That's a whole debate in and of itself, how a company could be profiting off of sins, but for me it's something to live by. There are things I do not want on my conscience.
2.) I prefer stocks that pay dividends, but it's not necessarily a deal breaker.
3.) I usually buy into companies that make products or offer services that I use and like.