You should probably check out this to get a better grasp of what is considered effective in the metagame. I wouldn't suggest going much farther than the OP, most of the forum is nominations to move ranks of certain Pokemon.
Other than that, use the Strategy Pokedex on the main page to get a general description of each Pokemon. I'd suggest Scizor, Terrakion, Landorus, and Keldeo to start looking at. There's plenty of resources on-site, it'd be more beneficial for you to lurk and learn yourself than me just tell you and have you use the same Pokemon over and over.
A good start would probably be here.
Other than that, use the Strategy Pokedex on the main page to get a general description of each Pokemon. I'd suggest Scizor, Terrakion, Landorus, and Keldeo to start looking at. There's plenty of resources on-site, it'd be more beneficial for you to lurk and learn yourself than me just tell you and have you use the same Pokemon over and over.
A good start would probably be here.