how you climb depends on how technical the trail is, how steep, how sandy, how rocky, etc. sometimes if you sit and grunt up it's best, sometimes you need to stand to get that extra power. that is difficult if you have to pick your way through rocks or step up a rock going up a hill. in general you need to keep your weight balanced between front and back. too far back and your front wheel tends to come up. too far front you lose traction on the back wheel. usually you have to shift weight as you climb, give some traction to the back wheel, give some traction to the front, etc. i assume you know about "rowing" your way up the hill, where you pull on your handlebars as you push on the pedals. i like to pedal as far as i can get, and walk up the rest of whatever hill i'm climbing. i don't mind walking, i have nothing to prove.