Prayer

Though the prayer alters are not yet implemented, you can still bury bones for Prayer experience. All you need to do is hold them in your hand, and shift-right-click the ground. Just about everything you kill will drop bones, and as they are non-stackable, they can fill up an inventory quickly. Bury them often, and you will level up fast.

There are a great many prayers that you can invoke (Ctrl+K, or H if I'm not mistaken...) just by clicking on the prayer's symbol. Each prayer has it's own perks from regenerating health, or improving your armor, to smiting enemies that attack you.