Start with both hands on the same rung. Lift your feet off the ground and with one hand, travel up the rungs one by one for at least several rungs, or as far as you can reach. Then come back down the rungs one by one, ending with both hands on the starting rung again. Then repeat with the other hand.
For instance:
- Both hands on rung 2
- Left hand rung 3, right hand stays on rung 2
- Left hand rung 4, right hand stays on rung 2
- Left hand rung 5, right hand stays on rung 2
- Left hand rung 4, right hand stays on rung 2
- Left hand rung 3, right hand stays on rung 2
- Both hand on rung 2
Do not crimp hard or use your thumbs. Use an open-handed crimp grip and let your thumbs just be bent, not grabbing or pinching the rung.
Make this easier by using larger rungs and/or putting your feet on holds and/or traveling up fewer rungs.
Make this harder by using smaller rungs and/or traveling up more rungs.