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That's pretty much how I used to do it, and that explains why the lines are so thick, expect I draw my lines with only one pixel thickness from the start. Then once the image is open in MSPaint, I use the straight and curved line tools to go over them again, smooth out the curves and add some finishing touches. It is a pain and takes a while, but the result is very fine, thin lines.

To add a background, I color it on the blank render with a predetermined color, let's say blue, then copy the entire thing. I open the background I want in another MSPaint window, select the blue I used to color in the background as my secondary color by right-clicking it, and then paste the render as an transparent layer. Usually every pixel that's pure white would become transparent when the colors are set as black over white, but when another color, our blue, is selected as the secondary color, every pixel that's blue becomes transparent. It's easier than it sounds, and is an effective way to paste a render onto a background without having to recolor the horses themselves.

Hope this helps somehow!

Yes, I work with different layers. First I search for a screenshot. I resize it with PhotoFiltre, than I open it in Paint.NET. Than I create a second layer, where I draw the lines. When finished, I remove the background and save the lines (including white background) as png. I open it in GIMP where I soften the lines (like this: http://www.animationsource.org [...] f-lines-using-gimp-t35860.html ) and than I open it in PhotoFiltre to colour it. I do the shading there as well. When I want a background, I open it again in Paint.NET, delete the white background with the magic wand tool and add a background (screenshot).

Well I was hoping to be able to help you out, but I'm not familiar with any of those. When you do the rendering, do you use multiple layers? The find that that's the easiest way. Just add one layer over the image you want to render, then draw the lines on that layer. Once you're done, go to the background layer and erase everything. By the time you're done, only the lines you drew should be left. Then I save it as a PNG image, open it in MSPaint, and soften out the lines.

Thanks, Bluehawk! I'll take that in mind.
I use 3 programs for rendering: Paint.NET, PhotoFiltre and GIMP. It's a lot, but I know how to work this way. I use Paint.NET to draw the lineart, GIMP to make the lineart colour-friendly, PhotoFiltre to colour and than Paint.NET again to add a background.

Nothing else I can say unless you want to add a signature, but with a blank background like that it's probably best that you don't; when someone tries to paste this image on top of a background, the signature can get pixellated around the edges and look back. If you uploaded the render with a background, then yes, definitely add a sig, but, like I said, I wouldn't worry about it for now. Just some advice for the future. BTW, what program do you use for rendering?