I have started to do this again too. It is freeing, isn't it?! I like to draw with pencil or charcoal, more than collages or paints as it is easier to take with me places. For inspiration/subject: sometimes I do things in the environment/objects, people, recreate things from memory that I saw, patterns or designs, or just images that come to my mind. I will also try my hand at doing mandalas; or if want something simple, finding the mandala patterns, and simply coloring for a mindful distraction. There are a lot of free mandala patterns online.
One exercise I learned was to try to create an image of the mood that in, and what it would look like you could see it in that moment; or collecting collages of images that show the mood in or if want to feel differently/better, what images would that mood look like to help feel better.
No matter the subject, have fun with it and enjoy!!