You can get rare candy by getting Battle points when you have rare candy just give them to your Pokemon to level up by one hope that helped or use an Exp. share and battle with stronger Pokemon
You don't. Battling is how you level up.
cheat or buy rare candy that levels up your Pokemon
Train your Pokemon and level them up by battling.
You level up by battling wild Pokemon, Trainers, and Gym Leaders.
I say just keep battling weak pokemon or normal ones
You level up your Pokemon, by battling around the sinnoh region, just like any other Pokemon game
keep battling Pokemon and people
Not all Pokemon require you to battle and level up to battle. For those that do, Rare Candies can usually be a simple method of levelling up quickly.
yes by battling the elite four
Mostly the 2 only level upers: Rare Candies and battling stronger Pokemon with your defensive.
the same way you would as other Pokemon, by battling, or by exp. share
You cannot. Whatever you can do in the game naturally (i.e. leveling up normally, by battling and using the rare candies available) is all that you can do to level up. The only methods to level up faster involve cheats.