Copy and UnCopy.
Don’t know where to start? Go and find a piece of work that you like or that inspires you and figure out how to recreate it. For music you could go through it line by line or bar by bar and duplicate each element for yourself. For a painting try to re-create the piece using the same methods as the artist. Once you have finished, the challenge is to use what you have just learned to make something new. This may feel like a roundabout approach but the objective is to get your creativity flowing and borrowing some from a source of inspiration can help do just that.
If you are a writer and love a particular book, can you transpose the setting? If the original was set in a London cafe, how would it be different if it was set in a New York cafe? Think of the different lives the characters would have had to lead.
If you love everything about a dance your favorite dancer has done, if you changed the music to a similar piece how would you need to change the choreography to fit? Some elements might transpose directly but others may need to be shuffled in their order so as to fit the music, or slowed down or sped up.
Creative play using the same rules that someone else had established is a great way to get started on some thing new, as your start point is something you already love.