What do motivational thoughts do? They help you take action. This isn't about positive thinking or motivating quotes. Those have their place in shaping your attitude and thinking. However, what motivates each of us is unique, so you need to have your own thoughts - those which are most effective at getting you going.
"In the middle of difficulty lies opportunity" - Albert Einstein
Motivational Thoughts Of Your Own
Making it your own means experimenting with a good thought until you find a way to use it in your own recipe for motivation. Suppose, for example, you're in a difficult situation and don't feel like dealing with it. As you sit there, you play around with the idea of opportunity coming from difficulty. Fortunately, you discover that it pulls you out of your slump to think about yourself in the future, explaining to a friend how you turned the difficult situation to your advantage. This is how you create your own motivational thoughts. Now, it might be more motivating if you imagine yourself being interviewed someday about how you overcame this difficult time. The thoughts that work for you are the thoughts you need to be thinking.
Learn Your Motivations
Experiment and get to know how your mind works. I find that beyond just thinking a thought, if I explain it to someone, I get excited. That is my own self-motivation recipe. When I feel unmotivated about writing, for example, I explain an idea I have for some article to my wife. By the time I am done, I'm very motivated to work. You can get creative in your motivational experiments. Maybe thinking about being poor makes you get up and get to work. If so, that is a great motivational thought. If visual thoughts are more motivating than mental conversations, then use those. See pictures in your head that get you going. Perhaps when people say you can't do something, you do whatever it takes to prove them wrong. Then it might be motivational to think about them saying you can't.
When there is a truly uninspiring task you have to do, try promising yourself a reward for completion - make it one that really means something to you. Keep that thought in your mind to keep yourself motivated. A trip to the beach and even a simple bowl of ice cream may be some of your more powerful motivational thoughts.