Strength & Conditioning
Being in the weight room will help in so many ways. Being able to increase your vertical, take contact going to the basket, fighting over screens, and injury prevention. Stay consistent in the weight room at least 3 times per week. Get with a trainer with experience if you don't have the funds you can youtube workouts "ways to increase my vertical", "strength & conditioning workouts for an athlete"
Get in the right reps
Being efficient on the court is key. Playing at the highest level comes with alot of moving without the ball, being able to catch and shoot, understanding the pick & roll, and making reads off of set plays. (set plays = plays your team runs). Most times on offense you will score will 3 dribbles. Remember when working out to go with the same intensity as the game.
Know your position
Going into high school you should start to focus on your position. If your a shooter, than you should be focusing on shooting from different spots, different curl/screen situations. Point guards should be focusing on learning on how to control the tempo of a game, how to run plays and put players in position.
Build a good first impression with your coach
First impressions are everything. Get off on a good note with your coach, be early, shake his hand, ask questions, stay humble, and be willing to listen and learn. You may have outsiders in your ear but every high school coach in the USA has rules and expectations. To succeed in this game of basketball you have to deal with challenges.
Watch film
Watch your film, look for your mistakes. Could you have taken a better shot? Was someone open? Could you have got over that screen instead of switching? FIlm is the best teacher, learn from your mistakes
Study upcoming teams and opponents. Players who played well last season, watch to see what worked for them; see what you can add to your game from theres. Look for open lanes and advantages you find in the game