The simplest way to use focus for me is to just put all spells in as follows

/cast [target=focustarget] fireball

That example will cast fireball on whatever the player you have focused is targeting.

so write a macro:

Code:
/target name  
/focus
*where name is the player name of the toon you are running as leader and selecting targets with*
or simply /focus your leader manually every time

Then put all your spell macro's in the style of the the first macro. This will give you basic focus targeting, after that I would find an in-game friend with some macro knowledge to help you out. Preferably a multi-boxer with some experience though that may be tough to find on some servers, what server are you on?