I've personally spent a lot of time examining my own motivation. I built a project called Deep Thought https://www.deepthoughtapp.com/en/keywords/motivation/

I have several techniques:

- Be kind to yourself

- Be comfortable with not finishing everything you need to do today

- Break down large tasks into smaller tasks

- I break down the small tasks using https://asana.com/

- Complete smaller tasks to gain motivation/momentum

- I try to use other smaller tasks (not related to the project) to build momentum

- Break up my day into time slices

  - Gym for 1 hour

  - Work for 1-2 hours

  - Lunch for 1 hour

  - Work for 1-2 hours

  - Some other activity for 1 hour

- I use my Apple Watch timer to trigger me to move along

- You can use a time tracking of sorts. I've been trying https://clockify.me/

  - I use tags to indicate what I'm doing:

    - Relax

    - Play

    - Planning

    - Research

    - Programming

- I set in my calendar times for

  - Breakfast

  - Reflection

  - Work

  - Gym

  - Social