Reference from real life whenever possible.
When you reference or copy from another artist's studies/sketches/art, you may be copying their mistakes as well. Furthermore, an artist's studies are their notes and --just like with history or chemistry notes-- copying someone else's notes will not help you fully understand the material. To completely understand anatomy, you must take your own notes and build your own understanding through observation.
This is probably a no-brainer for many artists but... scruffynerfherder and I were talking about this last night, and with the increase of "anatomy studies" showing up on dA's front page, it's been on my mind. DA's resource category has some great material, but I also feel like there is a lot of misleading information taught by amateurs who really probably shouldn't be teaching things like shading or anatomy, because they have a less-than-stellar grasp on it themselves. I'm not trying to knock anyone here, but it's a bit tr