I played a rogue, so you never stop moving, so it's easy to know what's around you. For target swaps I would just deselect, then when you get into melee range of your target you hit your main attack (which is macro'd with /startattack) so you automatically pick up your target.
It wasn't ideal, but separating movement and skill activation really helped me learn to stop clicking.
Nowadays (although I'm not playing any games atm), I use my G13's joystick for movement (as forward/backwards/strafe).
I could literally see the difference on Atramedes as melee. Everyone else would be clunkily running around the sound circle thing and losing dps, whereas I just moved in a smooth manner and never lost any damage. I honestly believe it gives me a huge advantage.