Start small. I can’t stress this enough.
Everyone sees successful games out there, and think they can make the same thing alone. Start by making a very very simple game. It can be a rock-paper-scizzors game, or a pong-clone. It doesn’t need to be fancy, and have 15 different game modes and online play.
When you finish the game, move to a new one, which is slightly different, or a completely new genre. This time a lot of the organizing will be easier to do, so it will be easier to “fit it in your head”.
Working on the same project for months, or even years, can be very tiring, especially if its one of your first projects, which has more chances of not being a hit.