This page outlines some key strategies for competitive battling that you may want to use, and should be familiar with before playing. To check what moves a Pokémon can learn, use a Moveset Searcher.

There are three main strategies for competitive battling:

Offensive

Offensive teams rely on outspeeding and damaging the opponent directly. This kind of team will often utilize hard-hitting Pokémon and use resistances and immunities to switch into attacks rather than having any walls. These teams will often use lures to eliminate counters, stat boosting moves, and stealth rock. The suicide lead is an expansion of the quick Stealth Rock concept and is often used by offensive teams. Suicide leads are common on offensive teams (e.g. Aerodactyl) - they stop the opponent from setting up Stealth Rock and at the same time set up their own Stealth Rock.

Balanced

A balanced team relies on many different types of Pokémon. Balanced teams normally have a few sweepers backed up by walls and/or tanks. Most balanced teams use entry hazards. The most successful balanced teams are often focussed on ensuring a successful sweep by one team member. Jirachi is a very flexible pokemon with great typing - it is often seen on balanced teams.

Stall

Stall teams focus on residual damage: sandstorm, hail, toxic spikes, spikes, and stealth rock. The majority of Pokémon on a team like this will have good defences and contribute to the overall goal of indirectly fainting the opponent's team. Stall teams normally feature at least one ghost to block Rapid Spin (a move which removes entry hazards: toxic spikes, spikes, stealth rock) and often have a shuffler with roar/ whirlwind (e.g. Suicune) to take advantage of the preserved entry hazards.

And there are loads of roles each Pokémon can fill:

Sweeper

A sweeper normally sets up with a move like swords dance, and then sweeps through the opponent’s team, knocking out as many Pokémon trying to revenge kill as possible before fainting/ switching out. They generally maximize attack and/ or spec. attack and speed, with all other stats being less important. Priority moves are handy for killing faster Pokémon trying to revenge kill. Lucario is a good example of a sweeper.

Wall

Walls use a high base HP, and high base defence (eg. Skarmory)/ spec. defence (eg. Blissey)/ Both (eg. Cresselia). Some walls can manage without too much HP (eg. Shuckle), but they are normally not as good. Walls almost always hold leftovers. To make a wall good, they should be able to recover HP (recover/ roost etc. are ideal, but  do something useful while they are walling pokemon – they may have attacks of their own, but as they are going to be investing most of EVs in defensive stats, it is often more practical to give them toxic or something similar (protect/ substitute helps stalling). To make a wall even more effective you can give it haze (to remove sweeper stat boosts) or roar/ whirlwind (these also remove stat boosts – this is known as pseudo-hazing or phasing).

Tank

A tank is a Pokémon with reasonably high attack/ special attack, and considerable bulk - normally more physically/ specially defensive. They will probably come in several times and do as much damage as possible. They are less likely to have stat raising moves and more likely to have recovery moves so they will be able to fight for a long time. An example of a good tank would be something like Zapdos.

Baton Passer

A baton passer boosts its stats with moves such as calm mind, bulk up, swords dance or nasty plot, and then uses the move baton pass to pass those stat boosts along to another Pokémon. Substitutes and moves such as ingrain can also be passed. In my opinion, the best speed baton passer is Ninjask due to its speed boost ability.

Status Absorber

A status absorber will be switched in when you predict a status move. There could be many reasons that a Pokémon is fine taking a certain status – it could be because of an ability like guts or marvel scale, or an attack it knows such as sleep talk or façade.

Revenge Killer

Designed to KO opposing sweepers mid-sweep, they will normally have a choice scarf, but can have a choice bands, life orb or choice specs if they are already very fast. Often Pokémon filling other roles can effectively revenge kill certain threats, but purpose-built revenge killers come in handy. Gengar is an effective revenge killer.

Lead
Your lead is the first Pokémon that you send out in your team. They are normally designed to beat other common leads, and may also help the team by using stealth rock/ rain dance/ trick room et cetera. They often have a suicide move such as explosion/ memento/ destiny bond and/ or taunt, to stop slower leads using support moves. An example of a popular and effective lead would be Azelf.
Cleric
A Pokémon that uses aromatherapy or heal bell to heal its team mates. Celebi is an effective Cleric, with good defences and heal bell.
Trapper
A Pokémon which can either stop an opponent from switching out - via Arena Trap, Magnet Pull or Shadow Tag - or can KO them even if they do with pursuit. Dugtrio is a good trapper/ revenge killer when equipped with a choice band.
Wall Breaker

An offensively Pokémon designed to crush walls, allowing another team member to sweep rather than sweeping. This is usually done with powerful offense - often at the expense of continued sweeping abilities or speed. Wall breakers normally have mixed move sets (both physical and special moves) to destroy walls specialising in either physical or special defence. Infernape is a good wall breaker with swords dance or nasty plot.

Spinner
A Pokémon with rapid spin to remove opposing entry hazards (stealthrock, spikes et cetera). It is useful for a Spinner to have an attack that is super effective on ghosts to KO them when you predict that they will switch in on you to block rapid spin. Starmie can rapid spin, and is a good special attacker as well.
Auto Weather Inducer
While Groudon and Kyogre induce more offensive weather, the only OU auto weather inducers are Tyranitar, Hippowdon and Abomasnow, who create sandstorm or hail respectively. This kind of weather is better suited for stall teams.

It is important to think about type coverage when building your team: You should try to have a variety of resistances, so that you will have a Pokémon to switch into a wide variety of attacks. Offensive type coverage across the whole team is also useful: you will be able to threaten opposing Pokémon more efficiently if you have a type that is super effective on them.