To train Slayer efficiently, it is recommended that you begin after reaching 70-80 combat, with reasonable gear. Unless you are making cannonballs yourself, most of the time you won't be using a dwarf multicannon but rather using only melee or magic. This makes certain tasks such as suqahs and kalphites (unless killing the Kalphite Queen) almost blockworthy, as they have no notable drops and offer mediocre melee experience rates.