| The thing I don't get is why must you "train" to go rock climbing. I mean just go out there and start climbing. The worst that'll happen is you'll fall on your butt and you'll have to get up and try again. Real world doesn't just involve pulling upwards.
As for gym, the very best method for pull ups is to start doing them in sets.
Ideally, you'd probably want to do push ups, and pull ups and assisted pull ups and reverse pull ups.
Push ups: just push up from the ground. Try wide, narrow, and regular width.
Pull ups: Try chin ups and pull ups. And spread the grip width. Try lifting without wrapping your thumbs around the bar.
Assisted pull ups: Simply reduce the weight for pull ups by sitting on the ground and lifting upwards. You can also do dips.
Reverse pull ups: Ideal for larger sets and beginners. Simply start by pulling a chair up to the bar, put your chin over the bar, and let yourself down. Ideal to build strength. | 
