We have alot of work to do.
Leaf Blade ( STAB )
Coil ( Nice stat boosting, and you can't get swords dance till post elite four )
Light Screen ( Excelent move, that works well with serpirior's nice speed )
Reflect ( Same purpose as light screen ( only for physical moves )
Honestly, you don't need more than one move of the same type on a pokemon ( This is discluding stat boosters )
Flame Burst ( Once again, you can't really access flamethrower until post elite four. )
Shadow Ball ( If you didn't pick it up in the relic castle thats where its at, and STAB )
Flame Charge ( not alot of good moves are accesable right now that work for him, this is NOT meant to do damage, just to raise speed for sweeping )
Calm Mind ( Stat Boost )
After you finish the elite four, take out flame charge for energy ball. but for now you can live with having something to boost your speed so you can sweep
Earthquake ( STAB )
Crunch ( STAB )
Brick Break ( Beats the dark type guy )
Dragon Claw ( This is specifically for fighting N and Ghetsis, both who wield for strong dragon types, if you get reshiram, ghetsis's hydreigon isn't as bad, but if you got zekrom, you will definetily need krookodile to handle him. )
Bulldoze ( You don't have access to E-Quake yet. )
Icesikle Crash ( I know I spelt that wrong... STAB )
Shadow Claw ( Ghost person, and psychic person )
Ariel Ace ( coverage )
Psychic ( STAB )
Air Slash ( STAB )
Shadow Ball ( Coverage )
Calm Mind ( Stat booster )
Surf ( STAB )
Focus Blast ( For the Dark guy )
Blizzard ( No access to ice beam yet, but ice beam would be better post elite four )
Dig ( Coverage )
Alot of these move sets would be alot better if you were post elite four.
Don't know where to find some of the Tm's I suggested?
I'm pretty sure I didn't put anything down that wasn't accesible for you yet.