To become a Raven Marches DM simply post a game proposal in the game planning forums with a time (remember to note the timezone to) and a brief blurb for the adventure. Assuming that first adventure goes reasonably well you are an official Raven Marches DM. The only reasons you might be asked to hold off is if you do not have a good grasp of the D&D 3.5 rules, in this event I am happy to go over them with you and you should be back in business.
Please try to roughly stick to wealth per level, you can work this out by figuring out how much XP your PCs are likely to gain, determining roughly what percentage it gets them towards their next level (use average party level or game level) and then figure out what the difference between the standard wealth per level from their level to the next is and giving out roughly the same percentage. So if I plan to run a 2nd level game and the PCs will get 1000xp, that is 50% of the XP to take them to 3rd level. The wealth per level for a 2nd level character is 900gp, for a 3rd 2700gp, the difference is 1800gp, 50% of which is 900gp, so each PC should earn roughly 900gp. These are not rigid guidelines, but checking them can help ensure you are not dolling out a ridiculous amount of loot. I imagine the Raven Marches will generally be slightly over wealth per level as a rule, but we do not want situations where PCs have double the expected wealth per level, etc.
Once you have become a DM I ask that you do not directly contradict anything posted in Setting information, otherwise you have pretty much a free reign. Do not make large decisions like having an army attack the city without first consulting with myself and others - on the forums. Please feel free to post maps, NPCs, adventures details, maps, here on the wiki. Link them through the setting page if you do so, or the adventures page for write ups.
I would also request that you follow the rules as much as possible, if your NPCs can do it generally the PCs should be able to do it - assuming they have the right combo of feats, templates, etc. - while this will not always be possible it's certainly encouraged. XP should be straight out of the book with small adjustments made if you go easy on the PCs or if the encounter is especially hard for some reason, for example advantageous terrain for the enemy. Roleplaying XP should be earned by RP, please do not give out 500xp for completing a 1st level quest with 3 encounters, for example, unless the PCs spend a significant amount of time tracking down information or persuading NPCs to aide them successfully, etc. We do not want a situation to develop where characters gain XP significantly faster in one DMs games because they give out loads of RP XP.
The world is designed to make every type of environment readily available, woods, swamp, desert, mountains, sea, town, frostfell. The world also has an Underdark which you are free to have your PCs enter, though I will be holding off for a few levels myself.
There will also be some overarching plotlines which you are encouraged to work into your games. The first of these is the upcoming election of Port Drambath's ruling body, known as The Crew. Intrigue surrounds these elctions where 1gp given to the town equals one vote, you might have your PCs hired by one potential Crew member to prevent another's funds reaching the Port in time for the election, etc.
If you do create an NPC for an important role, make sure you add them to the Setting page - for example if you create an NPC who is one of The Crew, or the High Priest of Pelor, etc.