How do you guys do it if you want to level up multiple skills for a sim?

I mix them like many above me have mentioned. Mostly though, that's for my own sanity. Staring at a sim standing at a mirror talking to himself for hours is no fun to me, so if I have a sim who needs charisma, logic and gardening I'm more apt to have him garden in the morning before work, then invite a friend over for a few games of chess and conversation after dinner. I'm a fan of leveling charisma by talking to sims my sims like to have around.