Preparation is as ever when starting any do it yourself project in the home.
Firstly clear the bathroom of all storage units and fixtures; this includes any blinds, curtains and towel rails.
The next step is to remove any toilet seats and shower screens; basically if you can remove it then do so.
This will prevent any damage to the items and will also give you much more room to work in.
A tidy environment means a tidy job.
If you have carpet or vinyl flooring then I would also attempt to remove this and the chances are you will be replacing it anyway.
Now disconnect any pipe work from the main feed, shutting off the hot and cold supplies at this stage will prevent any accidents which could (and will) create jets of water, and potentially dangerous showers of red hot water if you are connected to the hot water supply.
Once all the above is completed I would have a general sweep and clean up of the bathroom and then I would take a moment to have a break - put the kettle on! Now your bathroom should be ready for any alterations and installations you have planned.
Doing it this way may take more time in the initial stages but it will pay large dividends in the long run.
Most disasters occur when people attempt to begin a remodel in an environment that is not prepared correctly.
Accidents are most likely to happen if you are unprepared, so forearmed is fore warned.