In reply to lifeofphild:
Climb down as well as up! If I'm doing an ARC session on an auto belay I climb the same route 3 times up and down (may have to rainbow for feet on the way down) followed by 3 up and lower off (repeat for 15-20 minutes). Climbing down is definitely where I feel the pain! - of course this might be due to climbing for longer (say 8 minutes continuous as opposed to 2)
Assuming you know what your arms feel like when they're pumped solid (fingers uncurling, nothing left in the tank etc) call that 100%. For endurance training you should be operating at <50% pump, but for an extended period. this needs to determine the grade of route you're doing laps on, usually a good few below your onsight grade. eventually you should be aiming to do 20 minutes climbing, 10 minutes rest x 3 in a session.
50%>
Good news is as your forearm muscles are small they recover quick so it is possible to do a high volume of this kind of climbing provided you don't exceed the 50% pumpage guide, so 4 or 5 sessions a week are doable, if you have the time.
As others have said pay attention to climbing style - and make yourself pay attention to your climbing as you do it - silent feet on rep 1, hips in on rep 2, keeping the core engaged on rep 3 (you get the picture)
The endurance phase should take 4-5 weeks during which time you can read all about training for power, power endurance and probably injury prevention.
HTH
Andy
Post edited at 12:23