Medics are the only Troops that ignore flares. They only follow injured Troops, and if none of your troops are injured they just follow the closest troop. Keep this in mind when maneuvering your Troops because Medics will tend to move fairly erratically.
If there are no non-Medic Troops on the battlefield, the Medics will just stand still.
Keep Medics behind other troops so that defensive buildings won't target them.
Make sure you have at least 2 Medics on the battlefield, as they can heal each other.
A single Medic, however, is still able to heal himself, but only if he is healing a troop that is close enough to him such that he is affected by his own splash healing.
Medics do not work well with Zookas, as the Zookas have such low health that they can be killed in one hit by many defenses.
Medics and Warriors don't go together, as the Warriors are faster than the Medics and will leave the Medics behind.
When using Medics, watch out for Cannons and Boom Cannons, as the Medics can't heal as fast as those two do damage. This is especially bad since you will most likely be using[Tanks and Heavies with Medics, and both of those are bad against Cannons and Boom Cannons.