There's a book called Drawing on the Right Side of the Brain which is centered around the idea of drawing from life as a purely logical exercise--and it is. Beginner artists tend to draw what they think a thing should look like rather than how it is. For example, if you draw an eye you might be tempted to draw something like this, but a real eye would look much more complex. Learning to draw like that is a matter of drawing from life, photos, and what you see. You'll learn things that go against your tendencies as a beginner: that there are no hard lines, the way light hits an object and where dark and light should be, etc. You eventually build up a library of knowledge on how these different things really look and you'll begin to be able to manipulate these things without needing photos or references.