First off, I’d say your mesh is a bit too dense for the stage you’re at. You can get smoother results with fewer edges. Looks like you’re box modeling, and cutting in new loops to put in detail. Not a bad way to go, but I’d recommend getting as much shape out of as little geometry as you can before you resort to adding edges to your mesh.
I don’t know of any way other than pushing verts around to get musculature shapes (other than MakeHuman) but I think you need some references to inform some of the moves. (Wait a minute, yes I do. mr_bomb runs ribbons of mesh along the major lines of musculature, then fills in the interior spaces later. He’s got some video tutorials on making faces and making ears that show how he works.)
The sternomastoid looks pretty good, but the trapezius needs a lot of work.
The traps attach to the top of the shoulder blade and to the spine along the center of the neck, the traps on your mesh look like they attach to the point of the shoulder and the base of the skull. They do, but they also attach along the lines I mentioned. They need a lot more fullness in the back to look realistic.
The shoulders aren’t wide enough. It looks like you’ve taken the figure out to the end of the shoulder blade and the clavicle, but the spine of the shoulder blade that reaches around toward the front, that the clavicle rests on, and the ball of the humerus are all unaccounted for. There’s no delts, and no attachment point on the humerus for the pects in front or the lats in back. I don’t really know if that’s part of the shoulder or part of the arm, but it’s all tied in and part of what makes modeling this area so challenging.