Recently, an adult artist, looking to improve her drawing skills outside of the traditional classroom setting, asked if I had any tips she might use toward this end. The answer of course was, "Yes, lots of them." However in essence, they all boil down to only a couple. First, draw a lot. It's the old joke, "How do you get to Carnegie Hall? Practice, practice..." There is simply no substitute for "quantity" in terms of drawing experience. A good instructor looking over your shoulder helps of course, but this, by definition, places limits upon the quantity of work you can do if you only draw in class. I've found that learning to draw is a lonely enterprise. Perhaps it's best that way. To save time, draw alone and then seek critical evaluation from others whose judgement you value.
The other thing I would suggest is to develop equally both a "right-brained" approach and a "left-brained" approach to drawing. That is, using the right side of the brain, (which is highly visual) in drawing from real life, small things, big things, people, places, and things, in order to develop confidence and good eye-hand co-ordination, which, after all, is at the core of good drawing ability. Your efforts need not be slick or highly finished. Often this can be a waste of time in terms of improving your skills because it leads to a certain "fussiness" that tends to "tighten-up" your drawing technique which is not what drawing with the right side of the brain is all about.
However, as an artist, you will very often be working (for convenience sake) from two-dimensional sources, either photographs, clippings, or preliminary drawings. This is "left-brained" drawing, logical, technical, mathematical, and geometric. There are dozens of "tricks to the trade" in terms of cutting and pasting, scaling, collaging, compensating for photographic distortion, even (gasp) projection techniques, that every competent artist should have a handle on simply because they save time. Very often too, they are more accurate and their use may help compensate for a weakness in certain right-brain drawing skills. Many of these things, practised often, will also help develop good eye-hand co-ordination. In doing so, you will become a more versatile and well-rounded artist.