Its not clear if you intend this game to be a business or a hobby project (and there is nothing wrong with that - it's a great way of learning something new).
If you intend to develop this project as a business (very very hard to be successful in games IMHO) then start with the business side - who is your customer, how will you find them, what will they pay for etc. If you intend to work on this project as a hobby, then skip this part.
Business of Software Forum FAQ Business of Software WIKI Then I would, personally, start with basic programming skills before looking at anything specific to games.