definitely 2nd the recommendation for jamba. I can't imagine multiboxing without it.

It's fun to test it out with trail accounts. I can't even remember how many accounts I've left with 1 toon on them at level 20. But the trial account restrictions do get kinda annoying. Just simple things - because you never loot with your slave, you never have any money on your slave, so it starts getting diffucult to buy things - even simple spell upgrades get spendy. But it's still fun.

If you are just doing 2 accounts to play with, I wouldn't worry too much about getting macros perfect yet. That can be a skill all to itself. But for level 1-20 I just make all my spells hard coded. You get a new ability every level or two anyway, so you'll be redoing your macro's and "rotation" pretty often early on anyway.

#showtooltip
/cast [target=focustarget] <spellname>

That'll get you started assuming you have something macro'd that does /focus main. I just set my ~ key to /target <main>; /assist; /folow.

about 1/2 if not 3/4 of your time early on is figuring out how to make it all work for you. That's half the fun though and trial accounts are a great place to test things out without spenidn any real money.