I bop along and fix things that annoy me. I have contributed in the past to the Graphic Lab and may help in improving images from time to time.
You can request image improvement from me on my talk page. Requests made there get priority, unless I'm already working on something in Graphic Lab or elsewhere. When placing your request, please link to the image to be improved, as well as any other image(s) that may be helpful, and the article it will be used in.
Sometimes, I don't check Wikipedia regularly or can't take on more than the occasional minor edit. Your request may not get answered in a timely manner.
As a matter of personal policy, I will not create SVGs of non-free content—usually copyrighted logos and emblems—since I don't believe they meet the non-free content criteria.
I only accept requests to improve images that are useful and will be used. Sorry, but I won't crop a picture of your pet aardvark.
Perform miracles. There are limits to how much a picture can be fixed; if the graphical information just isn't there, there's nothing anyone can do short of repainting the photo by hand. Please don't expect a 200px, grainy jpeg to turn into a hi-res, featured image masterpiece.
Similarly, drawing hundreds of vector shapes of tiny details from small images is not my idea of a good time.