Hmm... maybe I should give Gimp a try? I usually use the desktop version of Paint.net for my minecraft texturing. I have Photoshop but I feel like trying to get Photoshop to work nicely with so small textures is like trying to use rocket engines to toast your bread.I use GIMP because it’s free and I think it’s reallt user friendly. Shading is a tricky thing, not enough and your textures look too simple but too much and they look mushed together. There are a couple ways I tackle this:
1) Use layers! I love putting all of the separate colors and components in separate layers. For example in the ranger texture I placed the cape, leather, straps, and base layer all in separate layers in order to adjust them seperately. This is also nice because I personally love tinkering with the hue/saturation and brightness/contrast settings. These give you an easy way to manipulate your textures without having to do it by hand.
2) Dodge and Burn. I love these tools, they make it super easy to shade the edges or add a bright spot in the armor. I will either use these with a small brush or use one of the messier brush options to randomly apply the tool. This is an easy way to give depth to your texture.
3) Color Variation: another good way of of adding shading to your texture without making it look like mush is adding colors that are slightly different from your base. That way it doesn’t all dodge/burn and blend the same way.
Hope this helped!
But these are some very good tips that you give here and which I will try to take in. I personally don't like using different layers because I always forgets that I'm working on a certain layer and try to do something on another layer.