This guy has three weaknesses, and noone is actually trying to cover any of them, so I'll do it.
Reshiram is weak to Ground, Rock and Dragon. Ground and Rock can both be covered by a grass type move, and Dragon covers Dragon.
Solar Beam It is the only Grass move Reshiram learns, it is very powerful, covers Rock and Ground, however, it is a little slow. I think there is an item that makes it a one-turn-attack. I think it is a herb of some kind, if you know, please comment on this answer.
Dragon Pulse/Dragon Claw/Outrage/Draco Meteor It is up to you which one of these you want. I would prefer Dragon Pulse over Dragon Claw due to Reshiram's high Special Attack, but if you choose Dragon Pulse, the moveset would not include any Attack moves, only Special Attack. Between Outrage and Draco Meteor, it is hard to decide, because they are both very powerful moves. Outrage causes confusion, and Draco Meteor lowers Special Attack, so if you choose Draco Meteor or Outrage, I would recommend switching out.
Fusion Flare and/or Blue Flare Blue Flare has a bad accuracy, but awesome power, Fusion Flare has high accuracy but not as much power. It is hard to choose, because they are both signature moves of Reshiram, which makes life harder. You can also have both of them if you want to, but true "Pokemon Masters" wouldn't agree with that, so it really is up to you.
Hyper Voice (If you're not having both Fusion Flare and Blue Flare) This is an awesome move and not many Pokemon can actually learn it, so I would be considering to have this move too. I personally prefer to have both Fusion Flare and Blue Flare, but it is really up to you.
I hope this helps.