Thanks to its ability, which lets it hit any pokémon with its STAB fire moves, it just needs two strong moves of its own types to hit anything for at least normal damage. Hidden Power maxes out at 70 power, which pales in comparison to some of the STAB-boosted powers of Resh's other attacks. Dragon Pulse and Fusion Flare end up doing about the same damage a super-effective Hidden Power does, and one of them will always be at least normal effective. Unless you have a specific pokémon or type combination you want to hit super-effective, Hidden Power probably isn't worth your time.
Other more powerful but (in most cases) less accurate options are Fire Blast, Blue Flare, Draco Meteor, and Outrage.
Its weakest point is its speed, so you're going to want a nature that boosts that, like Timid. Another option is to put on Nitro Charge; it might not be as powerful, but it will get your speed up on turn 1 to start attacking on turn 2, which helps you outrun just about anything without a Choice Scarf. So, Timid, Hasty, or Naive are probably your best bets; only use the last two if you really want to avoid lowering Attack.
What Vaporeon suggested for EVs is going to be your best option unless you have something unusual you want to do.