Cracks knuckles!!
Colouring is hard, good on you for practising!
Remember though, one of the first and formost rules in colouring properly - there is no such thing as a white highlight, let alone a white highlight on every single thing. Different surfaces have different textures that reflect light in different ways, and skin and, especially, cloth are some of the ones that reflect the
least amount of light. They shouldn't be swimming with shine unless absolutely everything is made of pvc!!
Instead of using highlights to define areas use shadows. And.... oh my god is that..... did you use the Burn brush.
REARS UP AND HISSES
Don't ever think of touching the burn or dodge tools to shade. Use them as sparingly as possible, for touching up areas you want to be slightly darker, or areas you want a light bloom on. Why? 1) It's lazy and you won't be learning how to actually paint with normal brushes which requires you to actually think about colour choice which is incredibly important with shading and colour. 2) It's a really gross airbrush tool and makes shadows almost filthy looking, because it isn't a uniform shadow - there's weird areas where you might have held it down longer but didn't get blended in properly and ugh it's gross. 3) It doesn't teach you anything about contrasting colours since it just either makes everything overly saturated or overly de-saturated depending on the settings.
DONT BE AFRAID OF CONTRAST!! Push your shadows! Don't just shade the very edges of thing, it's the first beginners mistake I ever spot. Consider the 3d form of the object - how does it wrap around the character? What are the contours? Shade those in. Follow correct shadow placement.
First and foremost! Use brushes for shading. Remember you can lower the opacity of the brush - choose a brush, choose a slightly darker colour than the base, and lower the opacity to block areas in. Choose the base colour again, and blend that sucker in. Rinse, repeat, with colours that get progressively darker, and don't be afraid to shade more than just the edges, that won't teach you proper shading! As long as you build up the shadows slowly it'll look more natural. Use the soft round brushes, or experiment with others.
This is my favourite brush pack which is one or two brush packs from DA artists slapped together for convenience, there's lots of nice soft texture brushes there for more detail and a more natural look.