The first thing you need is a passion for sketching as this is at the base of any animators work.
Start by creating your own characters or copying other cartoon characters and draw a small scene for them frame by frame. Some people like to start with their character bouncing a ball. You can use many things to do this like a small notepad you can easily flip page by page. The idea of the task is to make it look as smooth as possible as you flick through the pages.
Millions of frames go in to any animated programme or film you see on TV so you have to dedicated and have an eye for detail. You need to be able to achieve the same level of high quality with each frame.
There are many books on animation, try and get some out of the library and learn from the professionals.
There are many computer programmes you can use to create animation. Find out what the pro's use and try and get your school, college or university to get a copy as these programmes can often be very expensive.
For any art or film project for school see if you can do the project with animation. When you are looking at college and university courses try and find the best courses in the country for animation and apply.
Write to your favourite animation company and ask if they have work experience placements going. Even if you have to travel to do it.
Remember materials for animation can be expensive so try and get the most out of your school's equipment and materials.
Keep an eye on animation and media websites as there are often free courses run or jobs advertised in animation. http://www.csv.org.uk is a popular one.
There are many animation competitions so try and enter as many as possible.
Many TV channels are on the look out for animated shorts like the TV channel Trouble for instance.
Try and upload as much of your animation as possible so you can get feedback and exposure.
Always keep hold of everything you do from sketches to videos they are all good to show future employers.