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Intersperse the most important tasks with quick and easy things to give yourself the rewarding feeling of having checked that thing off your list.
Keep going. And then write a list for tomorrow that helps you get ahead.
However, there are some tricks that might make things a little easier, and maybe even coax out some motivation.
1) if you find a long list of todos or a large task that has a lot of parts, choose a place to start that you like or find most appealing. Example: if your task is to workout at the gym, choose the exercise you like most and start with that. A lot of the time starting is the hardest part, and by choosing the place to start it eases the way.
2) Break the task into tiny pieces, choose something ridiculously easy to start each task. Example: if you need to go to the gym, make the task to open the door. Make the task walking to the corner. Once you've started you'll be more likely to continue.
Motivation is hard to come by, and these tricks are just that. Tricks. They may help you sometimes, but at the end of the day you have to just remove excuses. Even ones that are valid. The gym was closed, work just ran over today, etc. You can do it!