All right, I’m not going to quote anything verbatim, because this is all pretty general advice that a variety of artists will tell anyone. Plus, who knows where they got it from to begin with?
1) Fully render one part of the drawing at a time.
Kinda, sorta… if you want to. Rendering one section at a time makes the artist pay more attention to tedious details, and the overall view is less overwhelming. The downside is that there’s a lot of prep work, because you’ll need to make a reference value to make sure you don’t have different values in one area as opposed to another; plus, if you’re drawing freehand, you might have some trouble with proportions.
2) Always do the darkest areas first.
This helps with maintaining values. Cool; however, I personally like to do the lighter areas on skin first, because it’s easier to darken than to lighten, especially with charcoal. I also like drawing hair (often dark) last. It’s a matter of preference.
3) Take an art program.
You can… there’s nothing wrong with doing so, and taking a program will likely fast-track your progress. You could also save your money and study independently and practice practice practice.