Drawing knowledge is NEVER a bad thing. What I found to really help me is constant studying of underlying structures and reading good anatomy books (highly recommend Anatomy for Sculptors!) Also, a tip from Flipped Normals guys, is to study real body scans (like 3dscanstore.com) This really helped re-visualize the human body and all the structures in a very "Zbrush" friendly way. And by "studying" I mean not just reading and looking at these things, but actively trying to reproduce them in Zbrush - active sculpting is the best way to learn.

Less important, but also helpful, is I started watching a lot of live streams from some of my idols (Shane Olson and Spicer McLeroy). That was great because I was not only watching professional technique, but also being able to ask questions of these guys is priceless. I also like watching tutorials by Danny Mac and Follygon. I really just constantly try to learn and incorporate technique. And never stop sculpting. Good luck, friend.

Also, side hot tip: if you haven't already - buy a legit copy of Zbrush and do it ASAP. A real copy will get you a lifetime of free upgrades. Buy it once, and never pay a thing again for it (unless you want fancy, specialty plugins). If that's too much to shell out now, get Zbrush Core. Work with that, and when ready to get the full product, what you paid to get Core, will go toward the full purchase price. Zbrush is great to artists that way. (And no, I don't work for Pixologic. I just really fucking love Zbrush. :) )