Wolfenoctis,Hunited,I have a lot of questions, so don't worry to answer them all:
How can I get better at making proportions?
Proportion is always relative, so for example the head has a certain size ratio compared to the torso and so too does the torso compared to the shoulders, etc. You can get better at it by studying your reference closely and trying to replicate these ratios, the more you practice, the better your perception will get.
How can I give a metal effect like the one in wolfenoctis's edit?
Study metal photo references, metal tends to have a broad range of values with bright specular reflections. Try to replicate the references, the more you practice, the better you'll get at illustrating metal.
Do I have to study art theory to make decent pixel art?(good enough to be paid for)
Yes you need to understand the fundamentals of art, pixel art is a medium just like painting or drawing and all the fundamentals apply to it just like any other medium.
Above all you need to keep doing pixel art on a regular basis, don't fear making mistakes, they are opportunities to learn. The only true way to fail, is to give up.
