Healing is an essential part of the game, but remember that it takes a turn. That means while you're glugging a potion, all the bad guys on a level are going to move. This can put you in real jeopardy if you're not careful. A good way to protect against this is to concentrate on upgrading your healing abilities on the first few turns. Up the number of hearts you've got, and get the boost that means healing potions are more effective.