Start with the big hitters- the major bones and the major muscles. Then add the next layer of complexity, where they attach, what actions they cause, their innervation and arterial or venous supply, their nerve roots.
The problem with this all is that you need to recognise there is a very real and hard limit on how much you can realistically learn and retain before it puts so much intellectual loading on your mind or eats into your time to the detriment of something else. I mean heck yes, you could know every muscle in the upper limb including the fingers and the wrist but that knowledge won't help you much in the end of year exam when you're supposed to know the details on shed loads of other content.
KenHub is very very useful to conceptualise structures and it gives hugely detailed information but you do need to know where to draw the line.