House Rule: Hit Dice

Forget what the book says for hit dice and leveling up.

Mages get a D8 for hit dice. Clerics, Rogues and Druids get a D10. Fighters (of any kind) use a D12 for their hit dice.

When leveling up, all player characters are automatically assumed to roll the maximum on their dice, so characters will get either 8, 10 or 12 HP at their next level, plus their Constitution bonus (if any).