There's a great blog that I follow called Muddy Colors and it primarily posts how to articles and elaborations on the contributors' works, which I find to be really usefull.

I didn't come into my illustration major knowing all the ins-and-outs of the professional world that I'd one day be jumping into, nor did I really think about how hard it may be to deal with clients or being creatively stumped. Muddy Colors has articles on all of these topics and it's both intimidating me and making me more knowledgeable about the world that I'll be working in.

One of the posts that I've read more recently is one about taking the time to make reference photos. I normally just try to imagine what the person I'm trying to draw looks like and how the light would work but I see the value in actually getting a reference photo, that way one can see how the light and proportions would really work in a real world.