Find a challenging project that is completely unrelated to art and see it through to the end, regardless of if that will take days, weeks or even months to finish. It should be something constructive that will help you in different ways, or that you have been putting off for too long. If it will take too long to put off everything else, break it down in to stages and complete just the first part, with intent to see it all through.
You will know what you want or need to create next when you are done.
As what Remleiz said, sometimes it's best to take a break for a bit to kinda refresh. I do know that switching gears and working on a different medium (like writing, cooking, or even organizing/cleaning) can also help break art block, and might also bring new ideas.
You will know what you want or need to create next when you are done.