If you want to have a huge song jackpot, you need to build the value of the song before you start it. You mainly do this two ways:
1. The 4 booster 2 ball multiballs (Pyro, Lights, Crowd, Amp). Think of these as the opening act of a concert. They are all stackable together so it can get crazy. If you do well in them, the song level (value) will be higher.
2. Locking as many balls as possible. You can see which band members have locked balls as their particular revolver insert between the flippers will be green. If you lock all 6 balls your song will have a high starting value.
When you start the song, you see the song level in the lower left of the big screen. 20 is low, 100 is good, 150 is amazing. You can build the song level as you play the song, but you want to start with as high a level as possible. People that don't know this will not usually get HUGE song jackpots.
chuckwurt The Power Chord Jackpots are nice, but the song jackpot is much more important. I think my max power chord is 4. That was pretty fun.