Okay, here are tips for the creation of VGC teams.
First and most important thing, this is Doubles, so stuff like entry hazards, set up moves and toxic, which are very prevelant in singles, are almost non exhistent in VGC, save a few exceptions. Instead, what you'll see much more is AoE moves and Protect.
Second: Protect. This is most likely the single most important move in VGC. Unless you are running a Choice set or an Assault vest, you WILL want protect. This can buy you turns if you are up agaisnt trick room/tail wind, and specially agaisnt terrains and weather. Predicting a double up on a pookemon and protecting it gives you a turn to do whatever you want with your other pokemon. It also adds synergy to:
Third: AoE moves. Earthquake is already the best physical move in singles, but in VGC it becomes much mroe devastating due to it hitting everyone on the field excluding the caster. Discharge is the same thing but electric type, slightly weaker and with a chance of paralysis. Surf is the same. For these moves, having a partner thats immune to these moves is ideal, but Protect allows pokemon that are normally weak or take neutral damage from these to save themselves from a teamkill and gain damage on the enemies.
Another kind of AoE are moves that hit only the oposite field. The most common moves of this kind are Muddy Water, Dazzling Gleam and Hyper Voice (less so in vgc2017 due to no move tutors). These don't require the synergy the likes of EQ do, but tend to be weaker.
The most important part of these AoE abilities is that they can hit the enemy even if they have a redirecter with follow me or abilities, which reminds me:
Fourth: Abilities. Many abilities gain more importance in doubles. Telepathy allows pokemon to not get teamkilled. Weather/Terrain abilities are much more powerful in doubles. Lightning Rod and Storm drain go from being an extra immunity with a boost to being essential to redirecting attacks aimed for your partners. Levitate allows for great synergy with EQ users. Perhaps the single most powerful ability in doubles however, is intimidate. Intimidate lowers the attacks of both opponents, and having an intimidate user on your team is increadibly important to check strong physical sweepers like Garchomp or hard hitters like Muk, Marowak, Snorlax and Kartana. This ability, couple with the burn status, is responsible for Special attackers being way more common than physical attackers.
Fifth: Items. As you guessed, many items gain extra importance in VGC, particulary Berries. Since VGC is played at a base level of 50, berries heal in bigger proportions. Sitrus berry usually heals half a pokemons health, and the 50% berries are great for pokemon with Gluttony ability. Resistence berries are also useful in a few situations. Due to this, and the short nature of fights, items like leftovers and black sludge don't find as much use. Choice Items are riskier due to the double up factor, with Scarf being the most used. Everyting else is about the same.
Sixth and final: Z-Moves.
While in singles the only z moves you see are support moves like partingshot, conversion and whatnot, with the ocasional Z-Fly being sprinkled here and there, in Doubles Z-Moves are great to furhter boost a move's power to make sure you can knock down a big threat on the other side. Z moves also have the added benefit of hitting through protect, albeit at a 75% decrease in power. An interesting factor of z-moves is that if you do a Z-Move of a AoE move, it will become single target, therefore skyrocketing it's damage potential compared to a normal move (For example, a standart 252 Att Garchomp using EQ in doubles cannot OHKO 252HP/0Def Muk, but with Z-Earthquake it becomes isngle target and can easily pick up the KO)
And thats pretty much it! The biggest threats so far are Garchomp, which can run a variety of sets, Koko with it's insane AoE, Lele with her insane single target burst, A-Muk with an increadibly powerful knock off and the ability to power through all the tapus, and Gyarados and Arcanine, the best intimidaters available, with gyarados being more of a set up sweeper and Arcanine being more of a support with Will-o-Wisp and Snarl, but with the ability to surprise with a surprisingly effective offensive set due to his large movepool.
For reference, here is the team I am using
Hope this helped