The first step to become an animator is to consider joining an animation course or study a degree in Animation at a good University.
Here you will learn the basics animation techniques like scriptwriting, storyboarding, timing, line testing, sound and editing.
Ideally you should have a background in art and you must enjoy drawing.
An important thing to consider while you are learning is to decide which type of animation you want to do, e.g.: 2d drawn animation, 3d, flash animation or perhaps motion graphics?
At the end of the course you will be able to produce one or several short animations and put together a show reel to submit to different animation studios.
If you want you can continue studying animation to a Masters degree or look for your first job as an intern or junior animator.
Good universities that offer animation courses are:
In the UK: www.bristolschoolofanimation.co.uk/
In the USA: www.schoolofvisualarts.edu/