Eq2 uses implied targets for harm/help spells. So if you first assist your tank then start on your dps or heal macros (with no targets in the macros) then your heals will land on whom ever the mob has targeted and the harm spells will land on the mob directly.

Any spells that have a friendly conditional will also pass through the mob to the mobs target. Conversely you can designate heal targets in your macros for ensuring heals land on your tank but these need to be adjusted for spell upgrades or grouping with a different tank. You can setup as many heal macros as you want to accomplish your goals.

Remember to make your first action for the healer to assist the tank. Keeping a mob target for the healer is required for the implied targeting to work.

I have a dedicated assist key seperate from anything else for all classes except the tank (of course), I put this on the same key as the tank aggro builder (for keymap purposes). Then split up debuffs, DD, aoe and deaggro spells into their own macros.

There are so many darn spell names/classes I can't say to just spam one spell i.e. Lightning Bolt. Currently the spell names change at certain levels so you have to check when you ding that the new spells you have learned are not named different. The major upgrades get different names, this is going to change in an upcoming Game Update, but don't hold your breathe.

Also check the wiki here. At the bottom of the main page is the EQ2 link and there is much more helpful info there.