I figured I'd share a couple of things I've realized and hope that some others might chime in with their own realizations or what have you. I'm going to have to preface with saying that if what I've realized is already well-known, I'm sorry. I suppose I should actually read rather than collecting things I intend to read at some unspecified time.
They always bothered the hell out of me because I never know quite where to put them. I've read that you should place them at points most perpendicular to the light source, but when you look at the way light reflects off of this surface and that, you notice pretty quickly that it isn't so. So, I took an object and marked off certain points on it and figured out how highlights work. I know I got it right because I can pinpoint on a cue ball where the highlight is from the viewpoint of another person in the room without the need to see it from there. Using a perfectly round surface as an example, here's how to know where they'll be:
1. Locate the point on the ball that is exactly perpendicular to the viewer's eye.
2. Locate the point on the ball that is exactly perpendicular to the light source.
3. Exactly midway between these two points is the highlight.
PERFECT LIGHTING (In theory)
Lighting in general is another thing that's bothered the hell out of me for the longest time. The most accurate way I've figured to deal with this problem is a bit of a problem itself, it's not for beginners or intermediates.(Which is probably why I haven't used it yet.) You'd need a keen eye, an exact hand, a good handle on dimensions, and a good understanding of chiaroscuro. But, if you got all that and you're going for broke without reference, the method should produce perfect results. Anyway, the idea is very simple:
1. Draw the contours of whatever your subject from the view that you'd like to be your final.
2. Draw the contours of your subject from another viewpoint, but this time, draw it from the point where you'd like your light to be shining from.
Why? Because if you do this it'd practically be a light by numbers kind of deal since everything would be marked off for you. If you could see from the point of a light source as it was shining, you would see no shadow. Any form that you couldn't see in the second drawing would be covered in shadow in the first. It's roundabout like crazy but it would be exact. Also, you should consider other uses of this method. For instance, say someone has commissioned you to draw their portrait. Let's also say that you're going to take a picture of them and work off of that. Problem is, the lighting is far from ideal and you don't have any lighting equipment whatsoever. What to do? Take a picture from the point you'd like to be your final. Take pictures from several other points while your subject keeps still to really get a feel for the forms. Then, take a few pictures from various points where you feel the lighting would make the most impact.
Anyway, that's all I got so far.