It’s hard to practice crack climbing where we live but it’s a good skill to have on the big walls. Here is some advice on technique from a real lover of crack climbing.
“No other form of rock climbing is more dependent on good technique. Face climbing is more intuitive- ever watch a ten year olds switch into mantles like they have been doing them all of their lives? Face climbing is climbing what’s there, crack climbing is climbing what isn't there. The idea of sticking hands and feet into that space (crack) between rock and then making them secure (jamming) doesn't have too many parallels in everyday life and that's why the whole process seems so strange initially."