Here are some of the common mistakes when you are starting to draw:
Sticking to one subject
As a beginner, it is understandable that you would like to draw something that you love or can relate to. Than is just fine, at first at least, but make sure you try out other subject matters too. Like if you love cars and started to learn drawing from drawing cars, once you think you’ve perfected it, don’t be afraid to venture to other subjects like portraits or landscapes. There is no problem with being good at one subject but the best thing for your drawing career is to expand to other subjects as well. For example: if you are good at drawing cars, why not try doing landscapes next, this way, you can add backgrounds and foregrounds to your car drawings.