Beginner looking for critique

It looks like you are doing great so far! Most of your sketches use the line of action fluidly and all the features properly follow it. Your lines also look very quick and natural, which is great! 

It looks like there are two ways you could improve your figure drawings moving forward. 

One is that you are relying on a circle as a base for the head. In some cases you have used a square shape, but it may be easier to figure out proper proportions if you use a more rectangular or oval-like shape using a single line to identify direction, but even then, the way you are doing it isn’t wrong, it just might not be as helpful. 

The second way you could improve is by allowing your lines to drag and flow into each other. You are already very good at this, but pushing it even further, especially with allowing your lines to be longer, would help a lot when determining proportions and forms after you finished the “skeleton” of your sketch. For instance, the way you are drawing the figures now, the lines determining the limbs are too short, so when you build the form of the body over it, it looks condensed. Legs and arms are always longer than the torso, and legs can be almost twice the length.

Hopefully you find these tips helpful! Let me know if you have any other questions and if this was sound advice for you!

Your overall knowledge of anatomy and muscles is good, but the proportions of the head and the body is slightly unrealistic. You should probably draw the head smaller and simplify the head more. Less is more.