Whenever I try to draw anything mechanical (especially mechas) it usually ends up as some simplistic weird looking thing that I'm usually totally ashamed of... (perfect for someone who's planning on making sci-fi.. -_-) But ah guess practice makes perfect.
Well, it's not only practice that you need. you also need to study, just like school. Study mecha and practice drawing them to get a feel for it. [link] Here, this is a great place to get some inspiration.
plugs have been cool to me ever since I witnessed Metal Gear Ray. These particular plugs are for storage (on the hip to our left) and weapon holster (hip on our right). The rest are modules. everyone knows mecha store fuel in their bladders.