Wall and ball
When you train by your self a wall is your perfect partner. You only need a ball and a wall. In the modern game of soccer it´s vital to have good passing and receiving and a wall will help you a lot to improve.
The wall never makes a mistake. If you give a good pass to the wall, you will get a good pass back, and vice versa with a bad pass.
Soccer training is all about repetition, you have to do the same training again and again. There is no better mechanism to build the muscle-memory necessary to master key skills then maximize repetition,
The wall is the perfect training partner, he can play with you for hours every day, and he never gets tired.