Animate!

I'm going to give the sky some subtle movement. First, turn the sky bitmap into a MovieClip in order to animate it independent of the hills:

Insert a Keyframe on the sky layer, move the sky a little (and maybe skew it, too), then Create Motion Tween:

Don't forget to add enough frames on the hills layer (so they don't disappear). Check my results..... then work on something you can be proud of: