I am not aware about what projects you have worked on before, but charcoal painting can be used in various artworks. I did charcoal painting on ‘still life’ which turned out amazing. You could also try making paintings on landscapes, portraits, abstracts etc. If you want more ideas then you can use Pinterest, where you can find various artists and their artworks related to your searches. Here’s a link for an example – https://pin.it/6kcvC0u