I would suggest having just 1 macro:
/assist focus
/follow focus
Then for all your spells, you don't need a macro. It'll just cast the spell.
When you want to change to your current focus target, hit that one macro, then use all your spells as normal.
In later levels, I found myself doing the following.
/assist focus macro for all my toons
Everyone starts attacking the mob, when it gets down to about 15%, my tank moves on the to the next mob, while the other are still dpsing until that mob dies. When the first mob dies, my tank already has some agro on the 2nd mob, hit the macro for the /assist focus to the 2nd mob, then start wacking him down.