>>528896864
my advice is to gather quality photo references, so you're not clueless about how something looks.
as for practical advice, learn the rules of proportion, how to measure proportions in a reference.
It's also a good idea to draw using krita line and square tools over your reference to have an idea of how the edge flow should look like.
It's much easier to not guess and just copy your reference with a drawn wireframe.
As for those textures, you should look up a texturing tool like armor paint (It's free if you can compile it) and just take photo textures and use a tool to downscale them to psx resolutions, like 128x128 and use gif compression exporting settings.