I'm going to be honest here:
Of all the "first flash submissions" I've seen, I'd have to say this one was really good. I'm not saying the movie was great, I'm just saying you're off to a good start. Your already better then the majority of Newgrounds so just keep practicing and one day, you will be a great animator. You can tween, and you can use sounds. Now just learn about smooth animating and that would be great. Just a word of advise, sprites show a very low animating ability, so try to sway away from them.
Happy flashing,
HOC