This is the first time I've actually trained and raised pokemon for a team, but be totally honest.

Venomoth
Modest Nature
EV: 252 Sp. Atk, 252 Spd, 6 HP
Ability: Wonder Skin
/Tinted Lens
Moves: Bug Buzz, Psychic, Sludge Bomb
/Quiver Dance, Energy Ball
/Sleep Powder
Item: Wise Glasses
You're not using Venomoth for what it's good at. Having good coverage with few moves thanks to Tinted Lens, and a wonderful setup combo in Sleep Powder and Quiver Dance.

Rhyperior
Adamant Nature
EV: 252 Atk, 252 HP, 6 Sp. def
Ability: Lightningrod
/Solid Rock
Moves: Megahorn
Ice Punch/Rock Polish, Hammer Arm
/Ice Punch/Rock Polish, Stone Edge, Earthquake
Item: Cell Battery
Lightningrod will negate Cell Battery's activation. Completely useless. I'd go for Solid Rock to survive super-effective physical hits more easily, and maybe a Choice Band/Expert Belt/Leftovers. Fighting has very similar coverage to ground, and if you keep Megahorn, it won't even be your best option against Dark types.

Scyther
Adamant Nature
EV: 252 Atk, 252 Spd, 10 HP
Ability: Technician
Moves: Aerial Ace, Swords Dance, Double Hit
/Brick Break/Return/Roost, Bug Bite
Item: Eviolite
Even after Technician, Return is about as strong as Double Hit and it doesn't miss. Brick Break will help you counter Steel types which resist both Bug and Flying. Roost for recovery as you're using Eviolite, it might help.

Rampardos
Adamant Nature
EV: 252 Atk, 252 HP, 6 Def
Ability: Mold Breaker
Moves: Crunch, Thrash, Iron Tail, Head Smash
Item: Float Stone
I suggest you ditch this. It's an inferior Rhyperior (cwutididthere.gif) and it doesn't do much to help your team. Float Stone is pretty damn useless, go for Choice Band/Scarf if you really want to keep it. Thrash is trash (cwutididthere etc. etc.), it locks you into a normal type move which doesn't help you against anything. Go for more coverage. Same as Iron Tail, it is inaccurate and has poor coverage. Fire Punch, Superpower etc. are much better options.

Ducknoir
/Dusknoir? LOL
Adamant Nature
EV: 252 Atk, 129 Def, 129 Sp. Def
Dusknoir has awesome defenses and poor HP. You should invest those 252 points onto HP, not defenses.
Ability: Pressure
Moves: Shadow Punch, Fire Punch, Ice Punch, ThunderPunch [B]Brick Break gives you perfect coverage with Shadow Punch, so you can have some room for more useful moves (Pain Split works pretty well with Dusknoir).
Item: Spell Tag

Muk
Adamant Nature
EV: 252 Atk, 252 HP, 6 Sp. Def
Ability: Poison Touch
Moves: Gunk Shot, Shadow Punch, Explosion, Disable
Item: Life Orb
I primarily use this team for double-battles