Plumbing repairs can get very messy so it is always a good idea to put down a drop sheet in your work area to avoid spills or more repairs.  Before starting any project i always like to make sure i have all the tools needed to complete the task.  Next is to make sure you have all the parts needed to complete the task.  Use a pen and paper and write down all the materials needed to complete the task.  A trick i use is i envision myself doing the job step by step that way i can mentally determine if i have all the tools and materials.  Next i would recommend locating the main shutoff to the house in case of an emergency.