Kudos for using the word "assiduous" correctly! Having a good vocabulary will help you be a better student - you can improve your vocabulary by reading more, or by learning a new word every day. There are many ways to motivate yourself to be more focused and hard-working in school.
- Making a good grade is always a good motivation
- Reward yourself for working hard - get together with your parents and ask them to help you plan a good reward, like a special treat at dinner one night, or movie tickets, or help buying something you really want!
- Make sure you are prepared for each day - always have your book, paper, pen or pencil, and any tools you need for each class.
- Get to know your teachers as people, not as "that mean old bat who makes me work too hard" - most of the time, if you understand a person as a human being with the same sort of good and bad qualities as your own, you are more likely to pay attention to them, and thus, to learn more.
- Watch the extra-curricular activities - it's good to have other interests like sports, band, art, or clubs; however, if your grades start going down because you have to spend so much time on the other stuff, it's time to slow down and get back to studying more.
- Remind yourself that, even though the school years seem to last forever, and sometimes you think nothing is ever going to change, realistically, school only lasts about one-tenth of your life - you are going to spend way more time in a job, and getting a job you will love will depend a lot on how well you do in school!
- Get creative and think of ways to make boring subjects more interesting! Ask the teacher if you can do extra credit work about something that isn't taught in the book, but that ties into the lesson. See if you can find something in the boring class that is similar to something you like. For example, if you find math boring, but you like history, try looking at ancient household finance records or population statistics. Imagine that you are an extraterrestrial learning about our planet and see if you can spend a whole class thinking like an alien (don't pretend so hard that the teacher thinks you've gone crazy, though!). Draw or paint scenes or diagrams to help make the subject interesting (see if the teacher will give extra credit for that, too).