Smooth Animation

Could people give me tips on making smooth animation. Iv’e tried using flashes tween class, iv’e tried using laco’s tween class, i’ve tried writing my own tween class, but i can never seem to get multiple smooth tweens. I.e. if i go past something like 4-2 animations (depending on type) at a time they start to get choppy and yet i have seen websites where they must have something like 5-8 animations going on at one time (for transitions etc.) and yet appear perfectly smooth most of the time.
The comp i’m on is reasonable and so shouldnt be causing choppiness (and its not the frame rate i’m using - i’m not a complete noob lol).