Capt. Jim said:
Be sure to get everything in writing. Don't leave out any details in you contracts with your GC, subs or suppliers. I always made my subs clean up their waste materials and dispose of them in my dumpster. Many subs will leave their discards right where they fall and not clean up. When this happens with your drywall sub, the cleanup is not fun.
Try to have your plans finalized prior to start. Change orders tend to be costly. Have your payment schedule outlined in your contracts, and be sure to stipulate any hold-backs. Partial and final releases of lien should be obtained each time you pay a sub or supplier. Be sure to file a notice of commencement. Certificates of insurance, also called CI's, are always required on my jobs. These are issued by the insurance company and are issued to you. They spell out the limits and types of insurance the particular sub carries (liability, E & O, worker's comp., etc). Licenseing, where required, is always imperative. Don't just ask if someone is licensed, check with the proper agency to verify. It is amazing how many un-licensed people here in Florida claim they are "Licensed and Insured".
I echo all that Shark said above. Most of what you can do yourself is related to your available time and your abilities. I would let my clients either do work themselves or be responsible for selecting the sub and being fully responsible for that aspect of work. This was never anything more than things like painting, landscaping, cabinets, flooring, or perhaps a pool. They usually had a brother, uncle, son, etc. in the business and wanted to save $$$ by using them.
I'm sure there's more to it than this but that's all I can think of righ now.
Good luck and keep us posted.