Alot depends on your set up but if the druid is melee this is how I do it when he is following my meleeing shammy. I bind the arrow keys as movement keys only to the druid. I have a macro key which is /follow <roguename>. All my druid spells/attacks are macro'd as

#showtooltip

/assist <roguename>

/cast <spellname>

/startattack



this way he is following the main already (like u had) I have the movement key bound so that i can take him out of autofollow if I want (stop follow) or control him entirely on his own if need be. When I enter combat he attacks how I want which auto stops follow and ensures melee attacking even if the attack doesn't go through. Post the battle I click my bound /follow macro (bound to mouse for ease) and I am on my way. I tend to hit that /follow macro often in combat too when moving between mobs, it has become integral to my fighting. Hope that helps some