Well, your question can't be answered unless you're more specific. Different moves apply to the different types of Contests, those being: Tough, Smart, Cool, Beauty, and Cute.
For instance, if you want a Pokemon to enter the "Tough" Contest, it is best to teach it moves such as Rollout, Double-Edge, Take-down, and so on. Likewise, moves such as "Charm" or "Attract" will do best in "Cute" Contests.
There are many helpful sites on the internet that will give you walkthroughs and FAQ's which should address your other questions. :)
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Feed best pokeblocks to your pokemon, Teach best moves for the contest your entering and just use the right moves at the right time.
i depends what moves you teach which Pokemon, but i would recommend a kyogre with surf, hydro pump, water spout and dive. i repeatedly won the master rank with it.
The three thunders. thunderbolt ,thunderpunch, thundershock.
I use Slaking it move are:Swagger,Yawn,Encore(or any cute move) and Slack off.I get 10 hearts in second round on all cute rank contest.(Except super rank I got 7 hearts)
A little girl will give it to you in the slateport pokemon contest room