Gamifying a subject will motivate you to work harder at it and even make it fun.
1: For subjects like maths, where the most effective study strategy is practicing questions, draw a roadmap for the number of questions you get right. Make it up to 1000, and have a mini reward each 100, like you get to have an ice cream, or whatever you want. Each 250, a big reward, like four hours of video games/ a movie night. At 1000, have something you’d love to do, plan a trip with your friends, something you would really look forward to that would actually motivate you to do more questions.
2: Subjects with essays: Use the grade you get in the essay as your rank. Update your rank with every grade. This will motivate you to work hard on every essay, and you’ll feel even better when your grades go up.
3: Subjects with rote learning (learning things off by heart)
Get a page with the number of pages you have learned off by heart. This way after a few weeks/months you can be like “Wow I’ve learned x pages off by heart”, and you'll also get bragging rights.
4: Languages that aren’t your first language
Set a goal for the number of conversations you want to have in the next month and break it down to a daily target that you know you can achieve if you try hard. This is by far the best way to improve your language skills, and it’s fun. Setting a target number of conversations will make it more fun and create some hilarious situations.