It really depends what you want to do with him. For the game I usually go all out offensive, because he isn't very durable. Moves like Fire Blast, Dark Pulse work well.
I like using him in doubles with sun support from something else, though, to take advantage of his ability when Mega Evolved. I feel Solar Power is more meant for doubles, because in singles the best sun setter is Mega Charizard Y, which you can't use Mega Houndoom with (for obvious reasons), and Ninetales is almost expendable as a Drought user and useless for most other things. Primal Groudon is of course banned.
Fire Blast is Houndoom's best move. Switch in on a Fire move to power up Flash Fire, use Nasty Plot if possible, and unleash hellfire on your opponents. Tyranitar and other Dark-types who have a second type that beats Houndoom (like Greninja) are its worst enemy.