It is really hard when that first set of muscles (and nerves, and actions, etc.) stare you in the face.
Like people say, flashcards can help, but I found I would make them and never use them.
I think you can save yourself a little time by using the Tulane "Human Mental Image" technique. It sounds real self-explanatory, but once you get the hang of it, you aren't really memorizing anymore.
1) First know where the bones are: spine, ribs, scapula, humerus, radius, ulna. That is the key, the skeleton is literally the framework of anatomy. Visualize them off of Netter, or your lab skeleton, or even on your own body.
2) Then lay a muscle down. E.g. - the supraspinatus. In your mind you should see it laying on top of the spine of the scapula, posteriorly, and the lateral end goes toward the superior humerus.
3) Now lay the neurovasculature down. What arteries/vein go under the SS? What nerves are near there and what nerve penetrates (innervates) the SS? One thing I didn't learn till late in anatomy is that nerve course matters SO MUCH. Where does it start, where does it finish? Where are nerves (arteries, veins) vulnerable to injury (in terms of a fracture, gunshot, etc.,) because that is how test questions are presented?
4) Now that you know where it is, you can deduce the actions. Since you know it is attached to the scapula and humerus, and you know the scapula is pretty much not going anywhere, if you mentally contract the muscle, the only thing that can happen is that you raise your arm. Now, think about what happens if you have a deficit? How is function changed? In this case, you know that initial abduction of the humerus would be impaired, but you also know that the other abductors can get you through if you actively initiated it.
Now, I know this sounds "Duh", but I was going nuts at the beginning with my damn flash cards. So, I opened up Netter, stared a bit, and did what our profs told us (outlined above). It worked really well. And if you see it on a real body after seeing Netter, it will totally stick.
I know it seems insurmountable, but 20,000 American MD/DO students do it every year, so I know you can do it too. It is just a pain getting started.
Good luck,
Simul