If you have any experience with roof repair or construction, you are trained in roof safety because it is part of being licensed and insured. Most companies provide regular education in safety techniques to protect the workers and the homeowner.
If you are the type to choose to do the roof repair yourself , you need to start with the basics, and getting up on the roof is the first step, we always recommend you hire an expert for this type of jobs, check here to find the right expert.
Ladder Safety
If you don’t own one already, buy ($200) or rent (about $30 per day) a sturdy extension ladder that extends at least 3 ft. above the roof edge. Aluminum is the lightest, but fiberglass ladders provide better protection against electrocution in case the ladder accidentally touches a power line or live wire. If possible, set the ladder on firm, level ground. On uneven ground, place squares of plywood under one foot to level the ladder base and then secure it with wire or rope tied to stakes. Fasten the top of the ladder with rope or wire tied to a secure anchoring point such as a 20d nail driven into a rafter. That will keep it from sliding sideways as you step onto the roof. If you are going to be remodeling the roof learn about dropped ceiling as well.
See more roof safety tips here...
Climbing on and off the ladder is the scariest part. Securing the ladder so that it cannot move will help, but always be sure there is someone there with you to help hold the ladder and also call for help if (God forbid) anything happens.
You would also be wise to use a helper to get materials up on the roof as opposed to carrying them up the ladder. Holding on tight with both of your hands will prevent slips and falls.