I basically as soon as it starts, pick up the bat throw it once to the right, quickly pick it up again throw it agian, then smash up + A then pick up the bat throw it up (to hit it) then do another smach up + A (if you time throwing the bat up, the bag will fall straight down where you were at) and then really depending on the character do small attacks on it (Peach, slap. Fox, gun, ect.) Then I smash the bag at the last half second. I usually get around 2000 ft every time. If you watch the video that game with the game where Lucas makes over 2000 ft you should get a general idea of how to pull off combos and such
And Keegzilla, what do you mean by strict time limit? If anything it is less strict. The time limit is still 10 seconds as like Melee but in Brawl you have a protective sheild so you keep the bag in so you can do more damage... But yeah over all I still prefer Melee's Home Run contest.