Whats considered a good keyword

[Snorlax]

With SEO it looks like you need to know somee keywords before hand. What is considrerd to be a good keyword? Is it something people search often or a singular word?

 

[Demon_skeith]

It has to be releated/tied to your forum's theme, so since you are after pokemon, something like pokeball or a popular pokemon name is what you want to use.