1. Staying motivated constantly is difficult. 
2. It's just about bringing the right mindset & tapping & keeping the right intellect fresh at the right time. 
3. Don't rely on motivation, but rather on constant pattern & rituals
4. A task too easy can be boring, a task too difficult can be discouraging.. Aim is to have right capacity task.. For peak motivation . (Challenging yet willing) 
5. Have a active motivation, be a motivator, & just begin because often a job completion is easier than just beginning it. 

Such information I found in this article by srishti sabharwal.. & for more steps to keeping yourself motivated is in the link below.. 

https://buddingpsychologists.org/how-to-keep-oneself-motivated/