Try making lots of different things. I'm not great at drawing, but I can paint up a model to look like it stepped right out of the setting it's from; I'm not great at designing video games but I can handle tabletop games like a raid leader handles whelps. I can't really write prose but I'm not the worst poet to grace the earth. Hells, my brother decided that he didn't want to write a story as extended prose so he wrote it up as though it were a play instead.

Also, decide why you want to make something. Do you want it to look cool, to make a point, to be something you can play a game on? Something interesting I learned when talking about Magic designers making flip cards: they didn't go "Here's a mechanic I thought up, what can we do with it," they went "Here are werewolves, how can we represent them?" If you're making something, think about what it's for, and that will inform your design decisions.