The details done on the green sections are wonderfully, and helps add focus to them. The pop of green in the eyes is also a great way to help prevent his face from being glossed over. The tufts of fur on his elbows are also a great touch.

One thing that helps with shadows is draw a circle that'll be erased later to mark where the light source is. This will help keep the source more set. I first thought it was from behind, but the legs indicate that the source is to his left.

There's some small errors here and there. One example is the left arm (your right) has a rounded bit to mark to help transition the arm and sleeve. The other arm lacks that, making an inconsistency. Another is the rather jagged lines. It's completely understandable, especially when being new to a medium. As you become more comfortable, smoother lines should come more naturally.

One thing to be mindful of is clothing folds. Having those around joints helps make it more believable. This will also help break the blockiness of the shirt. For pants, it'll primarily be around the hips/thighs and knees. For knees shirts it'll be focused on the elbows, shoulders, and hips/stomach. The amount and size will vary on material, so reference will be your friend.

Hope this helps!