Sometimes being given a topic is easier than having complete freedom to draw or paint what we like. If you have no guidelines then I would suggest drawing and painting what interests you. Sometimes we aren’t sure what interests us, so then it is best to take some time to observe life, nature, the weather, everyday life etc. and see what inspires us. I always find that going out helps with this, it is hard to be inspired when you are sat at home or in a classroom with the same four walls!
How about when you are set a theme for an assignment or project? One good way to start is to create a thought shower. Write down all the words, thoughts that come into your head on this theme and you will see one idea leads onto the next. A ‘mood board’ is another idea, cut out colours, patterns, textures, images that inspire you.
When I am short of ideas I use Pinterest to look at the work of other artists or images of a theme, don’t however be tempted to copy as this won’t lead to work that is unique.
Idea generation tips:
- Go outside, visit somewhere new, go to a cafe and watch the world go by
- Take your sketchpad and do some observational drawing and see what interests you
- Take some photographs
- Create a thought shower of words and thoughts
- Create a ‘mood board’ of colours, textures, mark-making
- Look at the work of other artists
Also see When I get Stuck What Can I Do?
rebeccaarttutor.com 
I’ve a book of uses for post it notes…. notes could link with the mind map in creating a wall scape ideas board.
Sounds like a great use for post-its!