Robot War Mech

for this one try seeing each element as a real volume , try to represent it on 3D , not just ' draw it ' , it'll help you place them better in space , also it is not really balanced , it can't really walk or anything in a realistic way. Use references is what I suggest , many people think that using reference is cheating , but all the pros will tell you that someone that doesn't use references won't be able to draw something well.
So if you draw mechas , search for mechanical pictures of machines , etc. Don't think ' robot ' , think ' machine ' , that's the best you can do to get a good design that works.
And if you want your designs to look more realistic , they have to be able to complete their task. Your robot can't really use his weapons , and he seems like he's ready to fall , he isn't stable.