Dear Beamzers,
first of all I beleive you really succeeded in conveying the creepiness and threat that this goblin emanates. You also are not afraid to do the detail work and that's really important! These are traits that are and wiil be useful throughout your artistic journey.
About what is the next step here is what is needed. I number them in order of importance. Go to #2 after you feel comfortable with #1 (not mastered, just comfortable), then #3 and so on. Some areas overlap and that's ok.
1) Anatomy. You need to do studies to get yourself better acquainted with the human(oid) body. If you want, you can study children in cosplay outfits if you want to jump straight ahead to the refinement of this goblin. The pose is ok, but your anatomy and foreshortening of parts (e.g. the left knee) need consideration.
2) Light/Shadow. These 2 babies go always together. Unless you want to go artsy 
These 2 will come from studies too, but you also need to read about theory (how light works) to better understand the magnificent and wacky (trust me, it is) thing we call light.
3) Color. This is the last. Color has a specific tint right? Brown pants, are brown right? Thing is depending on the light source there is a "filter" that alters it. So for example here, let's say you are lost inside a mine and this fella shows up. Your only light source would be a torchlight. Thus the goblin will be washed in an orange hue. Also you put a rim light. Rim light is amazing at conveying atmosphere but you used it as an outline. Rim light should hit only one side of this subject unless there's a light source directly behind it! Study color last, cause everything else is WAY more important.
You may ask: But where am I going to find all this information? Google is your friend, but if you want my personal recomendation, find Monika Zagrobelna's tutorials page and start from lesson 1 and do them all. She is hands down one of THE BEST and FREE sources of digital art lessons out there.
If you need further elaborations, I'm here for you. Be patient my friend and above all, enjoy the journey!
