Few things are harder than coming up with a good idea when all you have is a blank page. If you can't come up with a good idea, try brainstorming a bad one to get your creative juices flowing.
Sometimes you just can't force a good idea to pop into your head. Doing something is better than doing nothing, however. If you're at a loss for good ideas, try coming up with a bad one. Brainstorm it to the worst of your abilities. Trying to intentionally make something wrong can help you start to figure out the right way to do things. As UX designer Jerry Cao explains:
For starters, you're exercising your design muscles a lot more than just staring at a blank screen: designing badly is better than not designing at all. On a deeper level, designing a purposefully bad mockup forces you to think critically on the same topics, but from a different perspective. If you can figure out the worst place to stick a call-to-action, for example, that will shed some light on the best place. This kind of productive distraction allows you to think about solutions without actually thinking about them.
Of course, you don't have to present your bad ideas as good ones. It's simply an exercise to get you thinking. Thinking critically about a bad idea naturally leads to ideas on how to improve, so the more you can get your brain moving -- even if it's in a wrong direction -- the better the overall project can be.