Drifting an RC car is much easier than a real car. But, the type of car you have is critical.

[edit] Steps

Buy an RC car. Preferably electric (battery powered) but nitros can work too just cut extra holes to make sure the engine gets cooled sufficiently. 4WD on-road car is a must.(No buggies, truggies or trucks)
You can get special tires (Yokomo, Hpi, Tamiya, ect., ect.) make your own or wrap your tires in electrical tape.
To make your own get PVC or ABS 2 inch inner diameter, ABS gives a better "grip to slip" ratio. Cut them to the size of your rim and fit them on.
Go out in an open space.
Drive forwards and build up speed.
Turn sharply and floor the throttle.
The car should now be sliding, steer into the slide and use the throttle progressively to control the slide
Power out of the slide.

[edit] Tips

- Practice makes perfect, you'll have to practice to get the car to slide perfectly.
Be very delicate with the controls. Slight movements make the difference.
Start with 0 (zero) type courses, slowly to progress to figure 8 and donuts
if you can, try using drifting wheels