I do my normal maps in several stages and I work in Blender Internal when texturing and bake because it is more manageable and you can bake together several normal maps.
First i do projection painting from a real photo to get the bigger folds on the right place and then i bake the first normal map from a high resolution mesh with displacement modifier to the original mesh.
I do the smaller bump details in grayscale in photoshop, the seams slightly lighter and the french seams and edges soft dark. The average value of R:127 G:127 B:127 is neutral color for mesh surface level, everything brighter bump up and everything darker bump down. If you use gradients you should work in 16 bit to minimize banding. This image is then a base for the specular map but as 8 bit.
Finally I bake the bump on top of the folds normal map. In some clothes I have used several levels of details that I bake togeter for the final normal map.
I thought of making a tutorial but my language skills in writing are to "bumpy" that I use google translate for this And time is as usual in short supply.