We usually play with 2 house rules
1) No nukes.
However, we have relaxed the rules for rookie players and will allow them nukes if they so choose. Once you get the hang of the game though, that advantage is gone.
2) No attacking a human player until 1 AI nation is eliminated. If we get 5 or 6 human players at once, we might have to scrap this rule since we won't need AI nations.