Lighting/rendering help

[swift frost]

How do I fix the lighting on this artwork and make it look more convincing

[sleek pier]

Shadows. Im also not sure what brush youre using, but i would make the lighting solid as opposed to the softer brush you have. Then use midtones where needed

But your lighting will always fall flat without proper shadows because of contrast

[swift frost]

Oh ok thank you

[obsidian bear]

you also need a proper shading process here, you seem to just be adding light wherever instead of thinking about the shading structurally. most importantly you're not thinking about the line of termination (the division between the light and shadow)
rough example:

a head is a weird shape but it's sphere-ish, so in a very general sense the light is going to behave similar to a sphere (just with more bumpy parts disrupting the light shapes)

[swift frost]

Oooh I see

[obsidian bear]

if you look up references photos of faces with similar lighting you can get an idea of where the shadows should be. doesnt need to be super exact