Arms are unrealistically tight with the body. Legs are too long. Shorten the upperleg so that the fingertips touch the top of the knee, and scale the lowerleg accordingly. Make sure your feet fit about 1.5 times into the lower leg. Note that knowing proportions won't do. Whatever you draw, I actually recommend to find some sort of reference to get your perspective right. I tend to be able to draw a pose from a certain angle from my mind only if I drew it from life once, I don't know how this is for other people, but basically I'd have to draw every possible limb from every possible angle at least once to be able to draw anything without reference correctly.