Umm.The help I could say is,Line and color.Pretty simple isn't it?
But making weapons aren't very easy.Every detail counts,even the very small details that aren't really shown much should be properly done.And coloring is also hard.You'll need to have great color blending and gradienting.
Heed my tips or just watch this video
http://www.youtube.com/watch?v=29x3BukSiTI
Video is made by Peter Satera.And the video is 1 hour so grab a popcorn.