Instructions
Determine the purpose of your team. Knowing the reason why you are creating the team in the first place will help determine what type of Pokemon to choose. For example, if you are creating a team to beat the Champion, you might select Pokemon that have a typing advantage over the Champion's Pokemon.
Select the Pokemon you want on your team. Choose two Pokemon with an Attack base stat of at least 100; two who have a Special Attack base stat of 100; one with a high Special Defense base stat; and one with a high Defense base stat. Most of these Pokemon should also have a typing advantage over your opponent.
Give 10 Vitamins to each Pokemon on your team. Depending on the type, a Vitamin will grant 10 Effort Values to a Pokemon. The Vitamins you give the Pokemon should give them Effort Values in their stat. For example, Blissey's highest base stat is its HP. Therefore, you would give Blissey 10 HP Ups, which will increase its HP by 100 EVs.
Teach powerful moves to the Pokemon on your team. The moves you teach the Pokemon should have a base power of at least 60. Most of the moves you teach the Pokemon should be super effective against your opponent's Pokemon. For example, if you plan to fight a Water-type Gym Leader, you would teach the Pokemon on your team powerful Electric-type moves like Thunderbolt.
Train each Pokemon on your team to level 100. You can level a Pokemon to 100 by giving it rare candies, which raise a Pokemon by one level. Once a Pokemon reaches level 100, its stats will reach the maximum potency.