What everyone else said - play basketball.
If you can’t get anyone to play, do full court fast breaks all by yourself. Do the thing that kids make famous - get out and play by yourself in a fictional game. You do this at high speed you will not only get your conditioning up, but you will get game specific conditioning of changing direction, elevating for jumpshots and rebounds, and running the break with the ball in hand.
When I had to switch from football to basketball, I would go to a church gym or somesuch late at night and just play hard all by myself - pullup jumpers, posting up, fast breaks, the whole thing - all at competitive speed. It may look odd to an observer, but it was great to get in sport-specific shape quick.