When it comes to Pokémon battles I prefer to play casually. I've had my ass kicked by my friends far too many times to want to even try battling competitively. Still, that doesn't stop me from wanting to try and make my Pokémon the best they can be. I think just doing that is really fun. Here are a few things I like to do with my Flareon.
First up is Nature. Flareon is one of those trial and error type Pokémon where I screwed up the first time around when I had one in Pokémon X. I had the worst nature for it and I could feel it in Pokémon battles. Now I like to go with an Adamant Nature, which increases its Attack stat while decreasing its Special Attack stat. If you're concerned about Flareon's low Defense then Impish is another way to go. This increases the Defense stat while decreasing its Special Attack stat. Characteristics are something to keep in mind as well, but because they provide only a tiny boost, and I don't entirely understand how they work, I generally ignore them.
Next up is Ability. Flareon mainly has one Ability which is Flash Fire. This increases its Attack if hit by a Fire-type attack, but honestly, how often is that going to happen? It's okay but Flareon's Hidden Ability, Guts, is a far better choice I think. If Flareon is suffering from a status ailment its Attack stat is increased by 50%. While getting a Pokémon with a Hidden Ability can be a bit tricky I'd say the extra effort is definitely worth it. With the DexNav in Pokémon Omega Ruby/Alpha Sapphire it is easier to get this Ability.
Other things to look into as well are breeding and Super Training. While breeding isn't something I'm into too much, Super Training is fantastic and something I'm starting to use more. This tool was introduced in Pokémon X/Y, but it is also available in Pokémon Omega Ruby/Alpha Sapphire. It is great for getting those EV's (effort values) into the stats you want. Pokémon battles can be a bit random on where the stats go so Super Training is a great help to take some of that randomness away. I like to put my EV's mostly into its Attack, but I'll also put some into its Defense, Speed, and HP too. Special Attack I ignore because I don't really use it and Flareon's Special Defense is actually pretty good as is so I don't worry about it too much.
Last up is moves I'll teach Flareon. Unfortunately I don't remember any of the moves I taught mine right now so I will add them here once I start up Pokémon X or Pokémon Alpha Sapphire again.