Take notes in class & make notecards. Highlight important text . I'm in 10th grade and doing the John Baylor Prep course and he mentioned that whatever grade you're in times that by 10 and that's how many minutes you should be studying each night. For me since I'm in the 10th grade I need to study for 100 minutes. (10*10=100) . For you since you're in 8th grade you need to study 80 minutes every night. (8*10=80)
