This is as much a list for me as it is for my readers. And is probably biased towards painting.
Copy other artists work. This is quite literally getting a direct transmission from the artist through their work. You retrace their brush strokes and you learn how they paint. You will probably teach yourself completely different ways of making the same marks. Obviously in this case it is a STUDY, don't go around saying it's yours. This is done in art school ALL THE TIME so no need to feel guilty, plus instead of copying someone irrelevant to you, you can copy one of your favourite artists!
Go to life drawing class. Drawing from life is very valuable practise that can’t be replicated. You could draw your friends, get them to get naked for you and have a drawing party with a bunch of friends. Take it in turns being the subject.