How can I get straight A's? Easily distracted. HELPPPP?

I'm in Australia and I'm in year 7. Our grading works differently to most countries. Anyway I want to improve on my grades so I can have no worries for school. I want to be smart, I'm pike a C or a D student.. I'm not very good at school.. I've just started cello and I miss about two cles a week because of cello practises. Also calisthenics which I do is a mive commitment and it takes up pretty much my whole saturday and every week and maybe Sundays about six times a year. I'm saying All thus because sometimes I can't do ignments and projects on the weekend. My lockers a mess, I have half of the stationary needed for cl, and all my folders are broken and graffitied.. Can anyone help me with tips on being really organized and how to get straight A's . I want school to b easier. Thanks for your time, I really need answers!