planing and having a schedule of things still needed to be done.
Usually after a full days work at my actual job, I come home full of ideas and inspiration and spend as much time as possible working on my games.
I also write down my thoughts before I go to bed which helps me refresh my memory then next day, as it helps get you back into that inspiration and ideal flow state you were in at the start of the project. It's good to see where you are and if your meeting your self set deadlines, it also helps to have a list of what things are necessary to the game. That way you can check them off and it gives you a sense of progression
nothing kills motivation quite like feeling that you couldn't get it finished by the submission time.