Nice try
I can see 3 main points that'll greatly improve your work;
1) Speed up the framerate; 20-30fps (frames per second) is a good speed for a flash animation. Your current speed is a bit to slow, and makes it look 'choppy'.
2) Use separate layers for the people walking, and the background- that way you don't have to keep redrawing the background for each frame! (There's a button to create new layers on the bottom of the timeline)
3) Don't use the brush tool for backgrounds- the line tool makes for easier adjustment and looks less sloppy.
That being said- the best thing to do is take your time- never rush it, and practice.
PM me if you want any more help- or use at the flash tutorials on here.