-A group to play with. Aim for 3-5 usually, though smaller or larger aren't out of the question. Usually games with more players and players who haven't played as recently will have priority.
-An objective or adventure you want to do so the DM can prep it. If you need suggestions you can check out the Help Wanted! section which includes tasks from NPCs and PCs who need things done, but you certainly don't need to do something from the list.
After the Session
After the session the players will write up a brief journal entry detailing where they went and what they did and it will be written in the Longreach Log on the main page. Sharing information is crucial to making this a cooperative game and not a smattering of parties doing unrelated things.
In Between Sessions
If you want your character to do something between sessions like talk to an NPC, send another player a letter, etc. feel free to send the DM a message.