I agree that the most helpful info is that practice is what helps you get better and smaller stitches. Personally, I can't stand a polyester batting - it's too lightweight and doesn't provide enough resistance when trying to keep my stitches even. The needles "falls through" for lack of any other description.
I've always used warm & natural and while I like it, my current project has Dream Cotton Request. It's a lightweight cotton and I noticed that because it is a lighterweight batting, my stitches are smaller. I will probably be using it more often.
My absolutely favorite hand quilting thread is YLI. Gutterman in a pinch. Both are glazed 100% cotton threads. Don't like Coats & Clark, it frays and knots up too easily for my taste.