Here, have some redlines and comments, too. First, general ones:
- Start by blocking out the general pose with a stick figure. There's no such thing as art springing fully formed without doodly roughs and planning lines.
- Think about how an object is shaped three-dimensionally. Use references--ones that you can actually inspect in person (instead of just a picture) are best.
- The human body has some fairly well-defined proportions and ratios. Most people fall within one standard deviation of the average. The style of TF2 gives our characters monstrously huge hands and slight overbites, but otherwise they're pretty much normal.
Comments in specific:
- The neck is off-center, even with the original neck hole of the sweater. (I also prefer smaller neck holes, so I redlined it, but that's your choice to make.)
- The arms are too small. The distance marked "A" is the width of the Medics shoulders as suggested by your picture.
- The hands look weird to me. I'm right handed, but when I cross my fingers it's my left index finger that is on top. Also, the shape of his fingers look wrong. Trying my hands around a cup (as I assumed that to be the average girth of a dove), I found that my fingers barely crossed. Of course, Medic has much bigger hands than I do, but the way the picture has it still doesn't make sense given that he's cupping a rather fragile bird in his hands.
- The seat of the bench should be at an angle rather than viewed straight on. If you imagine a "camera" focused on the Medic's face, that means relative to it, the bench seat is lower than that, so there should be a slight angle to it.
- His elbows should have better definition, since it's a joint.
- His feet, while the right size, look too dainty. This might mostly be an opinion thing.
- Reference, reference, reference those doves. The dove in flight especially should look much more dynamic.