Select engine.Creating your own engine - the case is so complex that not every studio is taken for it.For example, the tool which created «Half-life 2» - «Source» was used more than 50 different games studios.However, programming directly to Source (as in «Unreal Engine» («Gears of war»), as well as on «CryEngine» («Crysis»)) requires a few months of training.There are tools like «Garry's mod» for the «Source», which can greatly facilitate the work of the engine - I would advise to take advantage of them.Pay attention to the FPS Creator.
Consider the setting.Clear "Imagine Peace", which will take place the events of your game (whether it be the distant f
uture, or virus-infected city).Think about the storyline and the main characters appearing in it.Try not to complicate too much action, but also to prevent the lack of plot.Take as an example of «Bioshok», where the scenario component is an important part of the game.
Determine gameplay features.Something that will "highlight" your rpg of hundreds of others.For example, «Portal» turned out to be popular because of the original concept, and «Half-Life" because of the constant variety - remember, the player all the time placed in the new situation and new enemies threw.On the other hand, the game about which you can say, "I'm somewhere already seen it" does not turn out to be so popular among the people.
Work on balance.It is very important that all of you conceived the idea could become a reality.For example, the developers of «Counter-Strike», though, and did a very popular game, made a mistake in one: incorrectly calculated the balance of weapons, which is why many of the "trunk" players do not enjoy at all.Therefore, in your own interest, to the entire contents of the future Action work the way you planned.
Assemble a team.Your opinion as the main developer, may be decisive, but constructive criticism is always needed.Moreover, other people can take a significant burden on the creation of maps, models and overall level design.Besides, since you will be able to organize brainstorming sessions and get the output is much better product than the one you would have done alone.