I try to do at least a couple anatomical studies every week. I'll generally focus on a specific portion or system of the body, so I'm not trying to tackle the entire thing at once. It really helps to focus on things that I notice I've been having a hard time with in recent projects.
These sketches are from a cheap cast I bought for around $15. But it's priceless when it comes to having a reference for this very complicated form! I'd definitely recommend acquiring one.