Sorry, I couldn't help but post something.
Don't use the gradient tool (if you can help it). I used to do this all the time, but you'll notice all your pictures look the same. Flat, and really weirdly colored.
If you want to learn how to really "shade" things, do it by drawing a SOLID color. No gradient. Just one color.
Then, after it looks okay with one color, add another color for "shadows" for the dark spots of your guy. If done right, you can make a guy look 3D with only using two shades. No gradients. Gradients are not the way to make your drawings look realistic.
After you've got two colors, normal and shadow, add in your third, highlights.
Now you can argue all you want about "I already know how to shade", "I already know how to draw", but just try it! You might like your stuff now, but try out a new way! Trying new things is the only way you get better. Even for the simple things like picking colors and lighting and shading.
If anything, avoid drawing outlines first. Outlines are a bad idea, you'll want to use the fill tool, which is TRAP when you're still learning to draw. You never get practice of painting in for yourself. Which is something you need to learn so that you can be comfortable doing fine details and shading.
Anyway, here's something I drew really fast, roughly based on your colors and shape. Might help you (the left one was the sketch). ROBO CAT.
