If a fixture valve or isolation valve is not available make sure the water can be positively shut down. A positive shut down occurs when the water is turned off completely. Whenever you are dealing with the domestic water supply make sure the angle stop serving the fixture or valve servicing a particular bathroom or area is shut off completely. If you are putting in new fixtures, faucets or plumbing equipment make sure you know what fittings are needed to make.

This may sound silly but fixture usage during repair happens more often than you think and it is very, very messy.

For example, safety glasses, gloves, Cool Gel and heat blankets (to make sure wooden studs don't start on fire). When repairing waste piping verify that no one will be using the plumbing fixtures during the repair. Materials (obviously) are another important part of any plumbing repairs. Copper water piping cannot be soldered effectively with water remaining in the line. If you plan on completing your own repairs, make sure you have the correct materials and tools.

If an isolation valve, or the main valve for that matter, cannot be positively shut down the repair or alteration becomes infinitely more difficult.