The key to pure crack climbing, as with every type of climbing, is the feet. I like to start from the basics, which with cracks, is the hand crack. Hand cracks are the nicest, easiest thing you can climb, so you can focus on body position and movement technique, rather than the more precise jamming. If you have never done a handjam, it will feel alien and bizarre at first, but just slide your hand straight into the crack, and flex it, especially the meaty area under your thumb. It will stick, and that’s a handjam. I always say, if I fall out of a handjam, I deserve it :), so I tend to run it out if I’m in solid handjams.