Self Improvement Made Easy

I don’t know why but for the past 4 years, I always leave something up to the last minute on the night its due even though I’ve had days, weeks, or even months to prepare for it. I’m a high-school student and I’m at risk of not graduating despite the fact that I’ve been admitted to some top universities in my area. What is some advice you can give me? I feel kind of helpless right now =(