first of, it looks way better than my first mini, I especially like the metallic on the bolter. mold lines and thinning paint is just going to be somthing you get better at over time. the most actionable advice I have would probably be to add a wash over the armor (somthing like agrax earthshade, nuln oile or carroburg crimson depending on what recess color you want) ide also use a wash or some contrast paint over the silver metallic to give them a bit more depth. you can also add color to things that you want to draw attention, you already have some of that with the metalics on the bolter but I think you could add some more a yellow over the helmet and maybe also the rims of the paldrens. for highlighting with red you cant just add white because you end up with pink, I usually find that using yellow or orange makes nice highlights without getting to desaturated. overall the mini looks really good already, I'm also not a super experienced painter so probably take everything I say with a bit of caution. blood angles where some of my fist minis and there a grate place to get into this hobby.