well
first of all, for a trailer, have some msuic in the back, like an erie typr of thing, and second of all, this reall bugged me, you didnt have a background!, if you want it to be successful, you MUST put a background in, otherwise its almost an empty animation, and also the gunshot at the end, get a sound effect for that... a gun blast is probably the most common sound affect you can get on the net.
i dont want you to be dicouraged from making the actual movie, because you have got potential, the art just needs to be touched up a little, maybe you could buy a graphics tablet? only if you want to make more animations, but you can get them for £20 on amazin, i dont know how much that is in dollars, if you are american, but its a really good thing to have if your serious about this.