Start with both hands on the same rung, far enough off the ground that you will be able to do a pull up. Then do pull ups as normal.
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 a larger rung and/or putting feet on.
Make this harder by using a smaller rung.
Why this over regular pull-ups? Any recommended hand distance?