''Any suggestions for finding a good 'universal' pruning basic concepts
guide? (Is there even such a thing as a unified pruning theory?''

I am sure there must be. I too would like to see responses to these queries.

Kam,

YouTube has some very good pruning videos that have been useful to me.

Prune back to a node. Try to avoid trifurcations if you can, by pinching out one of the branches. A bifurcation is a 'Y', a trifurcation is a 3-tined pitchfork - which is the normal growth habit of coleus, maples, jades, and scores of other plants. If you pinch judiciously, you can turn normally leggy plants into mounds of foliage.

I drew this up for the jade growers, but it will work the same way for coleus because of a similar leaf arrangement:

Al