D&Paint

I need to work on adding more shading to skin because in the picture it kind of flows together but as i paint it, you can't tell the difference without looking at brushstrokes. I'm having trouble figuring out how to paint her shirt because in the picture she's wearing plaid. I've started with the base color of the plaid which is a light blue but when i went on to paint the stripes on it, the shirt looked ridiculous..and still does :) any advice on how to paint plaid?