Fight as Super Goku
Intentionally allow one of your members to die at the final battle. For example, if you allow Kulilin to die (as in the story) Goku will get angry. He will flash, then turn into a Super Saiyan (BP: 4999999). If you give him a BP increase-card, Saityouruu worth 30 pt, his BP will reach 7999999). Goku cannot use his Kaikouken. Note: Do not allow Vegeta to die. Freeza may also become Super.

Easy Level-Up for Gohan
There will be a place in the first cave on the alien planet where a big ball rolls towards you. Allow it to hit your character; you will not die. If you have 6 HP, fight monsters and let them hit Gohan for at least 1 HP and do not die. If you have 5 or less HP, use a HP MAX card to get a level-up. This also may be done with Dende.

Note: Your BP, HP and KI will increase but not your EXP Level.