Well mate, you said you're riding a mountain bike? Which seriously does make it SO much harder! One reason, it probably weighs 5 or so KG's more than any trials related bike, and two, it probably has suspension? You don't want sus! Anyway, to the backhops, these will probably take you a couple of months to learn to do correctly and controlably. With the front hops, people who have been riding years can't even do them! They're not needed in any riding anyway to be honest.