Install a lock collar, a metal ring that fits around the outside lock cylinder. It prevents housebreakers from yanking the whole lick cylinder out. Two locks are better than one. Also make sure that they are at least 12 inches apart from each other. This will help reinforce the door in the attempt that someone tries to kick it in.
Vertical deadbolts are stronger that horizontal deadbolts.
Use a chain lock with screws at least two inches long. The links in the chaing should be heavy and welded. The chain itself should be short enough that the door cannot be opened more than an inch or two.