Although it is not necessary, many prospective Supervisors are advised to take part in the SPA Program. The SPA Program helps potential Supervisors improve their knowledge and skills on site.
Maintain a good attitude (which you should keep all through being a Supervisor) and always be willing to help when you are asked to help, edit answers and remove some flags, join a group!
For the power... (muh ha ha haaaaa !) I'm joking of course. The benefit of becoming a supervisor - is to help keep the site neutral and free from 'idiots' who are here to cause problems for the rest...
A SPA will complete 25 of tasks before being considered for promotion. This will consist of 5 Question editing tasks, 5 Answer editing tasks, 5 recategorising tasks, 5 tasks working with alternates...