Animationmentor has a lot of useful videos to help with learning the trade of animating. Also if you can get a hold of a video of the action your are trying to replicate I find that it would be helpful to use it as a reference. It will help you see the nuances of timing.
You're animations are not bad for starters. Better than how I started out XD
If I may give a suggestion, for your jump animation in particular, since that's what you seem to be working on. There's a concept in animation called Anticipation. It allows the viewer to anticipate the action and to make it look more appealing. Without it sometimes the animation is hard to understand without it. In the case of jumping the anticipation there would be to plant your feet on the ground before the leap. This can be done with just a split second bend of the knees, or knee, then leap.
Just keep at it and practice.
EDIT: I just realized the anticipation was discussed in the webinar link Mak posted. lol I kinda fail >< You could use the video clip there as reference for your jump.
