Animation is quite easy, but misstakes waste a lot of time :)

Bouncing and gravity symulations are very difficult. Check Ockham page:
http://ockhamsbungalow.com/Python/
You can find there some scripts which make your animation more realistic. You can either buy "poser physic" aplication.
If you are not experienced in "edit keyframe" window change all smooth spline section to linear. It makes your animation "rigid - robot like" but poser interpolation between frames can look worse. When you make base keyframes and main animation, change particular body parts in particular keyframes to spline sections. When you have legs IK on, always use line section on feet.

Preview never show you real time with all frames.
I always make few not rendered animations with few different FPS values. It takes few minutes or even few seconds, especially if you turn off shadows.
Before I start render whole animation I also check shadows making few short clips with 3-5 frames (for example "make animation" frames: 12-16 and 47-50).

Check your preview animation carefully, because it is terrible finding hand inside thigh after 24 hours of rendering.

Ref. Adoms advise - he is generally right, but body parts work different way in different characters. Anyways his tips help you avoid "jumping" wrist or elbow.