Natures
Adamant raises Attack by 10% and lowers Sp. Atk by 10%. It is applied at the very end of the formula, after IVs and EVs, so the higher the stat, the more the nature gives and takes.
The most common pick for a physical attacker: it has no use for Sp. Atk, so the drop costs nothing. Watch out only for mixed moves — Hidden Power and Weather Ball use Sp. Atk.
Flavor
Likes Spicy, dislikes Dry. This matters for Poffins, Pokéblocks and Berries: a Pokémon eats a disliked flavor reluctantly, and healing works worse.