IPC 2220 Series of documents provide a good source of info for design guidelines. They have tables for conductor sizes and spacing based on voltage and current, as well as general guidelines in regards to building for vibration robustness.
These documents won't give you all the answers- they...
Try www.ema-eda.com. They are a valued-added reseller of OrCAD products (fully licensed by OrCAD). They provide an online Knowledgebase, User Forums, white papers and tips, and offer training. I've taken training from them for OrCAD Layout which was very good. The instructor used to work for...