The easier methods aren't always the most benificial for experience: Get a good digital camera, lots of paper and pens, and be redrawing alot!
Or spend money on some transparent slides to overlay for characters, pain backgrounds but with cartoon characters overlain, possibly drawn and coloured in on pc.
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Study people in motion - Get some books that show the human body and different poses through progressions of actions - Even watch videos and copy scenes frame by frame, but dont just copy the 2d shapes, draw the 3d geometry as would properly draw anything.
And work. Alot,.
Too much for me to do.. I've only ever made about 10 minutes worth of animation if you sum everything i've ever attempted.
Lego movies are easier and somehow more affortable methods of animation though !!