So here's the little that I know... I wouldn't write just a major triad (CEG). Usually there would be a 7th too (CEGB). Then, usually, I would omit the 5th, or flat it, and add some upper extensions like a 9th(CEBD). So the chord sounds richer, with more color, but not too fat (with 5 or 6 notes), unless you want that effect. You can even omit the root, which give the chord a more ethereal feel. Moving from one chord to the next, you can keep some of the same notes too, and make sure the hands and ears don't have to move around too much. Transitions sound smoother. The upper note especially should not leap around too much. This, I'm told, is called "voice leading."
Factoring in substitutions, inversions, extensions, and the like, every chord has about a billion possible variations, but not all will sound good.