You can't use sleep inducing moves in opponent's Pokémon when there's another Pokémon in his/her team asleep. Yawn can't be used to PseudoHaze (make opponent switch) when there's another Pokémon asleep caused by you. When the asleep Pokémon awakes or faints, you're free to make another Pokémon of his/her team asleep. Sleeping being caused by Effect Spore or Rest are disconsidered from Sleep Clause.
You can't use two of the same Pokémon in a team.
You can't use moves that increases your evasion. Avoid the use of Acupressure, it has 1/7 chance to double your evasion.
You are strictly prohibited of using OHKO moves. They are Guillotine, Horn Drill, Fissure and Sheer Cold.
Don't need to explain, you are prohibited to use any illegally obtained Pokémon. Hacking parents to breed is also unaccepted, but people can't control this just looking at the stats. Hacking Pokémon with "legit stats" is also not allowed.
Uber Pokémon are overpowered Pokémon. Since these are "Standard Rules" you have to use the "Standard Pokémon".
The current uber list:
Deoxys (all forms)
***Note: In Standard Uber Battles, these Pokemon are allowed. In UU/NU battles, only Pokemon in the specific tier and below are allowed. This means you can use NU Pokemon on a UU team, but not UU Pokemon on a NU team. All other clauses are the same for a Standard battle that uses a different tier.
No Hax Items
These are all the items that relies on luck to activate. These items are:
Brightpowder, Focus Band, King's Rock, Lax Incense, Quick Claw, Razor Fang, Razor Claw, Scope Lens, Lansat Berry, Stick and Lucky Punch. Note: Scope Lens, Razor Claw and Stick are hax items, but they are the only ones allowed in competitive play, as they just increase the odds of something that can already happen.
You can't turn off your DS or move away from signal range to end a battle. People can have weak routers so don't always fight with the people if he/she disconnected. Not exactly a rule, but an ethic sense.