If you have a ball, you are ready to play!
If you don't have a ball, go get one - any ball will do, and if you are looking to practice on your own (with a wall) then cheaper balls are probably better (as kicking against a wall will deteriorate the ball quickly).
There are four core skills that can help you to play with the ball.
The easiest to work on by yourself is running with the ball. Grab a ball, put on the ground and tap it in front of you as you walk or run.
Another skill you can work on alone is striking the ball. It will help if you have a wall to kick the ball against (otherwise you will be doing a lot of running and collecting after you practice striking the ball).
First touch is another skill that will be easier to practice if you have a wall to kick the ball against. This way, you will be able to practice controlling the ball with your first touch after it comes off the wall and before you send it back towards the wall.
1 v 1 is the hardest skill to work on by yourself, but if you create obstacles to move the ball around, it is very possible.
Running quickly while in possession of the ball or moving the ball and yourself between opposition players and keeping possession.
Kicking the ball with purpose.
For example, short passes, long passes, and shooting for goal.
Controlling the ball as it first touches your body (using your first touch to make your next action with the ball easy).
Taking on another player to get past them and keep possession of the ball.
Taking on a player who has the ball to get it off them.
