This one already shows improvement from your legion cultist. It looks quite more clean, and painted in a much more controlled way. You seem to even have tried some cool effects on it.. Like OSL and NMM. Keep at it you will improve lots with practice.
To improve this piece you might try to outline the different armour parts with a lighter blue line, it is not easy and the first times will probably be a fail, but it can create a really nice effect. On some parts it will be easier if you don't use the tip of the brush but paint the line with the "belly" of the brush. Go look for some infinity game or 40K marines tutorial on google for some great advice. ^^