A brave choice for your first post and a pretty good start. As Ascension1223 said, thin paints will make a huge difference. Also try to avoid using too much pure white especially for bones, horns and stuff. Ink washes could also help to shade the mini and smooth out colours. Finally, it's always worth basing the mini - it doesn't have to be fancy but it has a huge impact on the overall look. Looking forward to see more of your stuff.
Good job for your first. You have picked out some details nicely (chaos emblem on the R shoulder, for example), but most other details seem to be lost in the dark paintjob. Highlighting other areas with lighter colors would really make them stand out. Also, mellow out the whites of the skulls and horns with a dirty yellow or a very dilute brown. Check out similar models with higher rank for inspiration - there are amazing paintjobs on this site (unfortunately none of them are mine) . Keep it up!
I like it, but there are a few improvements I might humbly suggest. First, the paint was too thick, way too thick so it looks very splotchy. Secondly, the articles on the belt, while important and stylistically diffrent due to their natures, stand out too much, and they detract from the mini. They need to be darkened, as the overall feel of the mini is sacrificed by their prescence. Go back and used thinned and mixed paints to tune up the appearance of your mini, additionally some more attention to the eyes could help, unless they are meant to be sunken holes. But I applaud your efforts and truly hope you keep painting, you show alot of promise. (p.s., as an amateur painter I can tell you alot of voters on this site vote both arbitraily and ignorantly. They all want golden demon winners, if a 5 is tabletop quality than this is certainly a 6. Don't let the votes influence your desire to grow)