Most important thing (or two):
- keep doing it, do at least one task per day, even if its as small as for eg. improving icon, or fixing some spelling or adding comment. Do ANYTHING in project ever day.
- do not change gameplay or type of game mid project. That means you keep experimenting and finding what is fun at very beginning, until you are sure do not invest time in “polishing” parts of game like content (maps), character design, etc. Yes those things are fun and less demanding, but doing this too early is almost certain waste of time.