How do I beat all the Pokemon contests?

Get a Pokémon with good Contest moves. (You can check contest moves under Summary) Then, feed it a lot of Pokéblocks to boost it's condition of beauty, smartness, coolness, toughness, and cuteness. Then, you enter it in Normal Rank Contests in Verdanturf Town. After it has won all of these, go to Fallarbor town and win the Super Rank Contests. After these are won, go to Slateport and win the Hyper Rank Contests. After these are won, go to Lilycove and win the Master Rank Contests. Then you are done!

That's obvious-get the highest score in each contest. If you need tips, here are a few:

Max out the contest stat of the participating pokemon (e.g., for a beauty contest max out the participant's beauty stat)
Use related move combinations (e.g., in a smart contest use two smart moves that make a combination such as future sight and psychic)
Prevent the other pokemon from scoring or lower their score (make them nervous, startle them, or attract the crowd's attention)
Keep yourself from being startled or unable to garner extra points
Maintain a raised condition
Make appeals when they are the most effective (e.g. use splash when last in line)
Do not bore the judge

You can win the beauty contests with a Wailmer that knows surf, dive, and water pulse. It will all four contest if you use the moves in the right order.

You can win the beauty contests with a Wailmer that knows surf, dive, and water pulse. It will all four contest if you use the moves in the right order.