The easier would be to have many intermediate goals. If you divide your project in sections, then you can create several objectives, many of them.
This is the method applied by several soccer coaches. If the goal is to win the championship, it is viewed as a far unattainable objective. However, if you only need to win the next match, it does not seem so overwhelming but achievable.
These sections may be chapters, different drafts with different level of details, main scenes that need to be connected later. How you divide your work into stages will depend on how you work, but the advantage of doing it is twofold: on the one hand, you cheat your brain by making it want to achieve a goal in a set date, but knowing it is not the end. You will have the benefit of achieving an objective, but you will still have the mental attitude needed to transition from one phase to the next. And on the other hand, if you are not able to complete this delivery in the planned time, you will have room to make adjustments to the following dates at the pace you are going, thus avoiding a bigger problem.
You may wonder, how do I know how long each stage shall last? But this is the beauty of setting your own goals: it does not matter. All this is a way to cheat your brain into doing what you want. As with most of the psychological tricks, you really do not want to know how it works, as long as it is working. The important thing is to set goals and then go for them, so your brain will get in the game and try to comply each time.
It is as important to find the time to write regularly as it is to be motivated to do it; the good news is that both complement each other.