You're goal is to cover the dynamic range of the shot. If you don't you will either have unrecoverable shadows or blowouts. Obviously, each shot has a dynamic range which will dictate how many shots and at what EV spacing. If you don't have a light meter, you can use the cameras spot meter to determine what the total range is or make sure to cover it by taking enough shots either side. Most on here believe going more than +/- 2 EV's is to much spread between shots and you're leaving something out of the shot. Some are ok going more, and some swear that anything more than +/- 1 EV is to much. One thing is for sure, if you don't take the shot at the time you're not going to be able to go back and get another.
My camera will auto bracket 7 shots, so I almost always shoot 7 shots at +/- 1 EV unless I think this may not be enough for the scene. I have used as much as 14 shots at +/- 1EV before, though these are usually facing into the sun at a sunrise or sunset and there's something in the foreground in shadow.