This is a wonderful article that was in the Washington Post about plate garnishing. I hope the link is still available and you don't have to do that bothersome registering to get to it. It's called "Step Up To The Plate", if you have to look for it.
The most important point when individually serving a plate is not to make it look like a TV dinner, where each component is clearly assigned a certain portion of the plate. There should be more flow.
Plus, it's pointed out that each element should be made to look as attractive as possible, hence, the addition of a bit of turmeric and black sesame seeds to the couscous or a few slivers of red pepper to the green vegetable.
Go, too, to the slide show in the article, (AUDIO GALLERY: Creating a Dinner Palette), which is a nice, clear demonstration of how easy it is to make the dinner plate pop. The only jarring thing in the slide show? The really hairy hand placing the final touches on the plate. Am I the only one to notice that?