Well, if you already have the sketch / messy lineart (?) finished, maybe you can try this program? --->
http://paintschainer.preferred.tech.
It's an online program that colors your sketches for you. So even if you have messy sketches, a bit of color might make it look better. Honestly, I just started testing it out so I'm not sure if it needs transparent images (the one time I used it, I did have a transparent image) or if it will just start coloring white space.
I can't really help much until you go into detail about what you want to fix? Do you want cleaner lines? Or do you just not know how to draw armored knights? Are your coloring / effects awkward? I used to use GIMP so I can probably help there but it would help if you stated the exact issue you want to fix.
Good luck!