No-equipment workouts are convenient and can build strength, but when you're bored with push-ups and squats, here are some advanced moves to try.
Gymnast Ryan Hurst shares some beginner versions of advanced moves on Greatist. They may still be super hard to start, but he gives tips on working up to them. For example, a "leg scale" (holding your leg out straight at different angles) requires a lot of strength and control. But once you figure it out, you're well on your way to pistol squats and graceful turning jumps.
Once you master these moves, you can move on to even more impressive skills -- for example, after you figure out the "double arm lever" in the photo, you'll have the foundation for other moves that require you to balance on your hands.
As a bonus, working on these skills will give you a great workout. See the full article for tutorial videos and extra tips.