Pitches are smaller part of a structuring out a game. Before you get around to creating characters or writing out stories or whatnot, you, the GM, can write up a small document to explain what it is you want to run. This document should be a single page- quick, simple and broad. You don't need to explain yourself in details, just make your players excited and curious to try what idea you've latched onto.
Here is a brief idea of template I thought of when trying to write it up:
Title: Big. Something that is unique to the idea, and more importantly, helps capture what you like to run.
For my upcoming game, the title for the game I planned was "City of Bridges." It refers to the main location of the game, the City of Portland Oregon. City of Bridges is a sobriquet for Portland- referring to the plethora of bridges in Portland, but I'm certain it isn't the only city to earn that name. And Bridges is an idea want players to think about, crossing rivers or other obstacles, a passage from one place to another. A metaphor to prep their minds, of sorts.
What Is The Game About? Yeah, you might have a great idea that should be keep hidden until the right moment- just go ahead and mention it. You don't need to worry about spoiling your plans or anything like that. The game would've been (and will hopefully be) changed by players interacting with it. If this idea excites you and is the main reason you want to run it?
That's exactly what you need to try and communicate to your players (and potential players). Get them to understand what you want to run, main big reason. That's all you need; people react well to passion.
In City of Bridges, the central idea of the game is excalibur, and the quest to try and find it. I wanted to have it be a quest that involved three separate time periods in three cities, all connected to the main group of characters in Portland. I went ahead and concided that my plan is to have the characters find or try to find excalibur and the search that surrounds that quest. I really like the idea of running a cast of characters in search of a uber-important macguffin. Feels like a kewl core idea to me, even if I admit to not having a clue to the how or why of it.
What System Is This? This should be the mutable, "I'm open to anything" part of the proposal... but yeah, we all have our own favorite system. Or a system we think will be ideal, and some players will be curious to know what exactly they are getting into. They might even have suggestions of better or alternate systems.
Ask for their advice, for something they might like more. Don't be afraid to drop your core ideal system to experiment. I've heard of plenty of people clamor or try to wedge 3.5 d20 into everything. Thats might work for somethings, but try to branch out. There's alot of systems out there- some might be easier than others.
For City of Bridges, the system I wanted to run for it is Mage: the Awakening. I like the idea of Excalibur being some occult metaphor to some, while potentially being a ancient artifact to others. M:tA is all about mysteries and power, and the core idea seemed grow best there. My players haven't offered a better alternative. I'm curious to try and alter M:tA a bit toward Fate Core, but that's for a different kind of discussion I think.
Establish When and How: Go ahead and try to set a date for character creation. Yeah, this should be obvious, but don't forget to do it, or at least leave contact information. Ask players for suggestions at this point too.
Add Some Fiction. If you have a creative bent, go ahead and stick in some sort of fiction about the game. This can be a introduction to the game, or maybe some flavor about the setting, that helps draw players in. It can be a fun way to express what kind of game you want to get your players into. It might finish the sale, for them, who knows?
For City of Bridges, I weaved bits and pieces of flavor about the setting throughout it. This included a mantra for Portland I've established in other chronicles set there, "City of Roses, City of Thorns; City of Bridges, a City Torn." It appears creepily from time to time, playing up a underlying theme of something going wrong in Portland.
I hope that helps anybody looking for some place to start for a Pitch. I've got some more work to do on City of Bridges, hoping I can get a Character Creation Guide for it too. Its good to sketch out and write documents like this for the games I run.
I like it, and the GM style I employ require me to improve alot, so I feel the need to get ideas written down as much as possible before starting the game at the very first make it better and easier. More information for me to fall back on, so I can help feed off the energy and ideas of my players. Good like and good gaming, :D.