I typically have my companions specialize in 3 areas each. Typically it'll end up with my pumping points into intelligence for them so as to increase the maximum in most party skills. Every 3 points in it increases the maximum for the affected party skills by 1. I also find I have an extra point when it hits that divisible.
One character will be specialized in spotting, pathfinding & tracking.
Another in wound treatment, first aid & surgery.
Another will be engineering and some other skills I forget.
For my own character I do trade, & leadership.
Any extra I have for companions goes into personal skills so they can make better us of horses, shields, bows of any type and move faster when on foot.