1. Setting! Perhaps the most important part. Setting defines (in most cases) who our characters are, how many zombies there are, how big of an outbreak there was, and possibly the eventual main antagonist if there is one. A lot of zombie apoc's start in sensible places, like East Coast or West Coast America, Russia, Germany, and places like that, because there's a high population and generally a lot of guns and weaponry. So our setting could be in one of those locations, or somewhere a tad more challanging, like the cold of Alaska, or other snowy places. Or perhaps Canada, where guns aren't as abundant (I did have a Canadian friend who always said that if there was a zombie apocalypse, all the Canadians would just go north! Zombies would freeze to death.)
2. Zombies! Second, or maybe first, most important part. Should we just go with the stock clambering zombie, with a slight twist, or something different. In a different thread Stormwarden talked about a 'Venom Apocalypse', however I'm not really a Marvel kinda guy, but the idea in general could be entertaining in a more realistic form. Or something like the new game The Last of Us (made me cry) where there's an airborne infection.
3. Style. Style as in, how should we roleplay it? Should we just do basic forum RP, where we post what are characters are doing in turns, or should we do it in a sort of D&D Fashion where we have a Dungeon Master who rolls a d20 to decide on things (I could do this, as I know how if no one else wants to). Or perhaps a dumbed down D&D, where each character does indeed have skill points, but instead of a game of chance with a die, the DM has you pass a skill check (Think: Fallout or Skyrim style speech checks. If you have 8/10 Strength, your chances of Intimidation are much higher.)
4. Optional setting. This last part is rather optional, as it'll more define where our characters start. An army base, a school (Think: Highschool of the Dead, so much fanservice in that anime.), or another place where our characters have more of a reason to stick together, and perhaps knowledge of who each other are before the apocalypse. This can have pros and cons, being that some of our characters might have set rivalries or friendships, however won't have the character development of meeting a new person, unless someone wants to have their character come from a different location, or joins later in the story.
If I missed any important parts, do let me know and I'll add them in. I've tried to keep this as simple as possible, so that we can plan it out quickly and get down to the RP. If it becomes something more folks'll want to do, we can add things to the setting later down the road. Sooner we fill in the blanks and all agree on it, we can RP this!