It sounds like you\'re trying out glazing, shags. You said you thin your paint, but how much? For glazing, you can thin as much as 10 to 1 with water. Also, how different are the shades that you\'re trying to blend? Theoretically, you could glaze a dark blue with white, but in practise, you need to glaze up through 4 or 5 intermediate shades at least. If you have too much contrast, then try glazing over the pesky line with an intermediate shade.
A bit of soap or flow aid in your water will help to soften the lines because the paint won\'t gather where it has already dried. Oh yeah, and practise, practise, practise.