If you want this in greater detail look here
These are basic rules and such with the VGC taken from smogon:
>''level 50 limit, which helps certain Pokemon do things they normally cannot do at level 100. Timid Max Speed Scarf Abomasnow normally hits 360 Speed at level 100; a +Speed Azelf will outspeed Scarf Abomasnow by 1 point. However, at level 50, the same Abomasnow will hit 184 Speed while the same Azelf will only hit 183 Speed. This is big as Abomasnow can now do damage to Azelf before Azelf can even move.'' ''Item clause is another change standard players may not be familiar with: each Pokemon must have a different item from one another.'' ''Formerly, the VGC had banned Uber tier Pokemon such as Kyogre, Mewtwo, and Dialga. Howerver, starting with this year's VGC, a new rule has been added to allow several of these Pokemon, with the only banned Pokemon comprising of the following: Arceus, Celebi, Darkrai, Deoxys, Jirachi, Manaphy, Mew, Phione, and Shaymin. The new rule allows players to use up to two of the following on their team: Dialga, Giratina, Groudon, Ho-Oh, Kyogre, Lugia, Mewtwo, Palkia, and Rayquaza.'' ''A concept that might seem foreign to singles players is the lack of entry hazards. Doubles battles are so fast paced and have very few switches that entry hazards are almost non-existent outside of the rare Stealth Rock. What this means is not only an increase in the use of items like Focus Sash and Pokemon like Shedinja and Ho-oh, but that you can no longer rely on including Stealth Rock and Spikes when doing damage calculations while creating a team.'' ''team work very well together, covering each other's weaknesses and hitting hard and fast. Trick Room teams make use of the move Trick Room, allowing slower Pokemon to go first for 5 turns, creating a powerful combination of bulk, attacking power, and speed that is tough to deal with. The last of the "Big 3", Rain Dance, is simple: use Rain Dance and sweep the opposing team with Swift Swimmers and rain-boosted Water attacks.''
Hope these ideas have helped you!