Field Medic Suggestion
Field Medic 30
Drag and heal your partner 25 times.
Heal your partner 25 times by holding the 'A' button when he's down. Training mission in Somalia does not count. You can also repeatedly shoot at him to bring him down (if you have the ammo) and then heal him to get this.
I don't know if this has been suggested yet or not, but the easiest way to get this is on Miami, either 2 controllers or online with a friend. Once you get to the power station and turn the power on for the monorail, you have to disable the power to the electronic lock for your partner to come back across. Leave the power ON, then have your partner/controller 2 walk across the wire on the bridge and he'll be put down and the power turned off. Revive him, then turn the power back on and rinse and repeat until you have the achievement.
The biggest perk to this is there's no enemies around to make it a pain in the ass. Hope this helps someone.