kk-
I will get you started with this:
http://assets22.pokemon.com/assets/...14/Play_Pokemon_VG_Rules_and_Formats_2014.pdf
You will need to read this over carefully, as it does give you the lay-out of what you will need to follow for the rules and format for playing competitively.
Once you understand the format and the rules (if you have questions about it- feel free to ask)- you can begin to set up a tournament at your location.
The tournament can be a "side event" sort of thing, as it is not "official" (meaning, it is simple league play for practice and fun) and just simply host one tournament during league.
Start out with a single round elimination structure. Players who win advance to the next round, the players who lost will not advance.
This structure is the easiest to begin with, and just let everyone know the format and rules before they opt to sign up.
Please refer to those rules, as they are official for TCPI events.
League tournaments can be set up in so many different ways, and it can be either competitive or for fun (but as always "fun" is the key), so if you would like some info on setting up a VGC 13/14 format or for fun (or both), let me know after you have read the link above.
I can help with anything you need to get started, so don't be afraid to ask- even if you think it is a silly question!