I don't know if you have played for your middle school of for the local CYO or youth leagues, but if you haven't, chances of making the JV will be pretty tough unless you are a special talent.
You see, most varsity and junior varsity coaches keep track of the kids coming through the system and, especially if they have been in their jobs for a while, they have communications with the youth leagues, AAU teams, CYO teams, middle school teams and just about any other team a local kid might play for.
Because of this most coaches looking at incoming freshmen already have scouting reports on kids and know who the better and special talent kids are. Chances are if you have played on any of these teams and are very good, the coaches already know who you are. If this is your first shot at organized basketball, there's little to no chance of you making the JV or varsity unless you are some phenomenal schoolyard talent that happens to have an unbelievable understanding of the game at a young age.
Sorry, that's just the way it works.
Now, if you want to make any team, it's real easy if you want to impress the coaches. Win every drill you can doing it flawlessly, don't cheat it. Run as fast as you can always. Always be moving. Always have you hands up and moving on defense and shuffle your feet on defense don't cross them. Communicate. Warn of picks, switches, call for rebounds, call for the outlets, call for the ball on breaks. Box out. Play smart and within yourself. Layup with your left hand from the left side and with your right hand from the right side. Hit your shots. Show no attitude and always do exactly what the coaches tell you to do, not what you think you should do or what you think they want you to do but exactly what they say to do.
Do all that and you stand a good chance of making a team. Your individual talent, athleticism and game knowledge will determine which team.
