Well, although I guess there is a torque rating for each screw, I do the same thing you do - tighten it until it doesn't turn easily - but not "over tighten."
But what does that mean? Well, to me, there is such thing as over tightening, and that's called "breaking." I have snapped screws before, and it's no fun thing because then you can't get them out!
My practical advice is to continue doing what you are doing, but just make sure that you use Blue Loctite before you start screwing.
Zachary