what are the principles to be An Animator 2D

you have to be meditating first, Good sketcher and imaginitive. then too much practice on analyze the animation keyframes and timing. you can start with ready made character like poser to do animation there and have the sense of time.

For the beginner, creating and working on small scale animation projects is a good way to gain experience and learn about the overall aspects of the animation process, including camera angles, sound editing, voice acting, scripting, character building etc.
As you are already familiar with various softwares it would be advisable to further enhance your skills in story-boarding, hand-drawn illustrations, vector softwares, cartooning styles etc.
also branching out and learning more about other various methods of animation and special effects is always an advantage

First you draw on paper your plane of animation and you have expert skill of software like Flash, After Effect etc.

First of all you have to get yourself familiar with the principles of animation, if you can draw already you need to know what and how to draw it, you can start with stick figures, when you draw a stick figure and it looks real and alive you know that you are a good animator.
The basic principles are all over the web, for example: http://minyos.its.rmit.edu.au/aim/a_notes/anim_principles.html then you have the advanced tips and tricks which you can find also everywhere, like: http://www.3dworldmag.com/2011/01/06/10-best-animation-tips-tricks/ and it cant hurt attending Webinars or online courses, hearing from accomplished people is always nurturing.
Good day