I suppose this is more of a writing tip but one tool I use a lot is the Kill List.

This is created when you are getting near the end of the project and is basically the list of tasks as well as additions and segments still need to be done. By this stage you should have everything basically ironed out and have a clear idea of what you want to go in the game and what you have decided not to include.

So a Kill List might look something like:

*Write 3 more scenarios. 

*Rules for alchemy.

*Revisit monster summoning rules.

*Check all playtest feedback.

and so forth.

The list can be quite long, I usually add everything to do it that I can think of and if you think of additional tasks ("Oh shit, I need a cover picture") it goes on here. What does NOT however are new features. By the time you write your Kill List you should be narrowed down on the feature set and things can only be dropped from this point on (within reason). 

The list can be in any format. I prefer to keep it on paper since there is a tangible sort of finality in crossing something off the list. 

When you have your Kill List, keep it in sight at all times when you work. Each day pick items from the list (as suits your schedule, I recommend doing at least one) and knock it out. Keep whittling down the list until you are at the end of it.