In order to make your pictures less fuzzy when you paint them, you need to spend some time on detailing the finer parts. You need to really flesh things out with gradually decreasing brush sizes for things to take form. I absolutely don't approve of my little pony, but I do approve of art improvements, so here's a little crit: You did a good job on the background and I think you should definitely flesh it out a little with a smaller, low opacity hard brush so that it gives your drawing more form, and you need to study the effects of light a little bit more. For example. I'd make the bright blue lighting a little bit more subtle since in real life, it would be more subtle since it is only a small part of the picture. Shade her first so that it looks like the moonlight is shining down on her (with some subtle white outlines around the lineart and shadows that suggest the moon is above her) and then give some subtle blue highlights as well. it could really help the picture. If you want me to help you see what I mean let me know, I will edit it and give you my redlines/

Heh, the light is quite a mess. I didn't really plan very much on this pic. I just added the background stuff randomly, which is also why I forgot to make the moon shine on her at all. So, I added the light sources after the light. << >>
The gradually going into detail with smaller brush sizes is a good idea. I'm still quite new to the painting thing, and I was always wondering how experience painters make all those details. :D