Here's how I have my keys setup:

F1 - All toons select tank
3 - All toons assist tank

Before pulling, I make sure all toons select the tank. Once combat has started and taunts are done, I hit 3 and all toons /assist and start casting their initial debuffs, etc. After that, I just go down the chain of spells/CAs.

If there are multiple mobs, I hit F1 in between kills to get everyone back onto the tank. Rinse and repeat until fight is over.

If the tank dies and I feel the fight is winnable with the remaining crew, I will manually target the next "tank" or whoever has aggro with the healers. I'll also manually try to rez up the tank. If it's a tough fight, however, I just Evac and start over.