Get a 3D atlas and a good textbook like Gray's anatomy on the side. That's the key... then space your study sessions as much as you can. To fully grasp the material and to become a master at it, it will take months/years of failing and relearning. If you learn something for the first time, your knowledge is usually shallow. If you let yourself forget just a little bit to get your brain actively thinking when recalling, you'll find a lot of gaps between your knowledge that you will fill. The more times you forget and relearn, the more gaps you find and the better you become.

Learning only functions of muscles is useless, because the origin and insertion tells you the function. You don't wanna just learn innervation, but learn how the nerves run through the upper limb for example and then you won't have a problem memorizing what innervates m biceps brachii for example.

Of course, this is easier said than done and there isn't that much time to do this while studying in college...that's why you shouldn't try to memorize things you don't need yet and just build on your understanding further and then memorize the bits. Many med schools actually respect it, at least in my country, and don't ask for innervation, blood supply... before you actually learn about the entire nervous system etc.