It's been said before. Climbing's all about technique; where you need to overcome the geometry of the bike, mostly the height of the front end which is optimalized for descents (otherwise, suspension is negligible).
Ass as far back as possible, while lying down on bars, to keep traction on the back whilst not wheeling. For tehcnical uphill sections, you also need to be in a relatively high gear so that you're able to pedal over the the rocks even in case of slippage. More aggresive tyres help with traction, though there's the weight right?
Imo there ain't anything more energy-consuming than technical climbs