Motivation can be both positive and negative motivation. Both work.
This may sound a little harsh, but take it for what it's worth.
My son had 3 main things motivating him.
1. He always met perfection with his grades, each year PUSHED him to maintain such grades. He had straight A's from 1st grade til he graduated high school. Including 4 years of the IB program. He played 2-3 sports a year, since he was in 1st grade. And the desire to win pushes for perfection. So by the time high school came along, he was committed to being all conference, all state, etc. He did achieve all of this.
2. Where we live is one of the greatest places to raise children. But it's one of the worst to graduate, stick around, and find a job. So, my son was highly motivated to be able to MOVE OUT and not get stuck in Mini-Mart, Walmart, etc. types of jobs. So, when classes got tough, he remembered his GOALS.
3. Finally; he kept a picture of his cousin, in his football uniform on his wall. His cousin, in the start of his senior year of high school, basically gave up on school. Went from a B+ student to almost not graduating. Finally graduated high school (Barely), couldn't get a job; tried joining the military "Lasted about a year and they kicked him out", etc. I asked my son why he kept his picture on his wall. My son's reply: "It Reminds me that I don't want to become a LOSER like he did".
Different motivations for different people