There are a few things I have learned thus far in the making of an RPG. My hope is that some of these lessons will help other upstarts get going in the process.
Do not make an RPG before you have a fully fleshed out Game Design Document. Some games can get away without having one, this one cannot. Also, realize that you are going to have to revise it over and over again, but don't get too hung up on the revisions, or discouraged that it always has to change. It's just a fact of life.
Have a good project management system. It's likely that a team making an RPG on any significant scale will not to able to do so alone. Establish a team, call your talented friends, look online, hire out if you have to, just get a team. Once you have the team make sure that the team is somewhat organized and at least one person knows what is going on with everyone. We use dropbox for all of our shared documents and it's kind of a nice way to get access to documents on the fly. The 2 gb limitation on the free account might get annoying, but probably not for projects on this scale.
Make a database. I would suggest looking at old tabletop gaming books and see how they establish themselves and base your database off of that. It should include the entire bestiary, with fleshed out descriptions, statistics (both explicit and derived), the amount of experience and gold they will give once defeated, who they can be grouped with, where they can be found and what they drop. Don't forget about all the special attacks and magic. A lot right. Yeah. Too bad the database also needs all advanced stats for your own characters, including a lot of projections about what level they will be at certain points of the game, taking into account the golden path player and the endless grinder. Look at how much gold the party will need to optimize their gear in the next town and base the enemy drops off of that. It really goes on and on and these are just a few tips. Our database ended up being about 15 sheets, averaging 30 columns and 60-80 lines. x * y* z = a hell of a lot.
If you guys have a local team, and I highly recommend this, have meetings. Meetings once every two weeks or so are good for morale, and also lets the whole team know what everyone is doing. It's also a good workshop opportunity where you can pick one task that needs to get done and do it collectively. Which brings me to my last lesson learned.
You probably have an assigned task on a team, but don't be afraid to dip into other things. We are indie after all. The hierarchy should be grounded but at the same time somewhat flexible. Sometimes your story writer has to work on the tileset, fact of life.
Last thing, take breaks after you established something. Go to the bar, don't get too wasted if you have to work tomorrow and talk about how great this game is going to be and how much it's goin to change your life. Talk about your dreams to move to LA and get hitched to some movie star. This is the time to do it, since reality will check in when the buzz checks out.
There have been like two RPG's on XBLIG that I have a great deal of respect for. I think both teams will be successful, and our goal is to not 1-up them, but to compliment them and maybe establish the platform most well known for zombie-avatar-fortune cookie-ninja killing-massage apps and turn it into at least a respectable place for RPG's.
As we get closer to completion, Ill post the game design document we have as a reference tool for new teams, and perhaps even the database upon completion.