Rate my team

I've won most of my games.

Politoed (M) @ Leftovers
Trait: Drizzle
EVs: 252 HP / 252 Def / 4 SDef
Bold Nature (+Def, -Atk)
- Scald
- Hypnosis
- Encore
- Protect

Dragonite (M) @ Life Orb
Trait: Multiscale
EVs: 248 Atk / 252 SAtk / 8 Spd
Rash Nature (+SAtk, -SDef)
- Thunder
- Hurricane
- Dragon Tail
- ExtremeSpeed

Starmie @ Damp Rock
Trait: Natural Cure
EVs: 252 SAtk / 4 SDef / 252 Spd
Timid Nature (+Spd, -Atk)
- Rain Dance
- Rapid Spin
- Hydro Pump
- Thunder

Toxicroak (M) @ Leftovers
Trait: Dry Skin
EVs: 244 HP / 252 Atk / 12 Def
Adamant Nature (+Atk, -SAtk)
- Bulk Up
- Substitute
- Drain Punch
- Sucker Punch

Nidoking (M) @ Life Orb
Trait: Sheer Force
EVs: 252 SAtk / 4 SDef / 252 Spd
Timid Nature (+Spd, -Atk)
- Earth Power
- Sludge Bomb
- Ice Beam
- Focus Blast

Volcarona (M) @ Lum Berry
Trait: Flame Body
EVs: 252 SAtk / 4 SDef / 252 Spd
Modest Nature (+SAtk, -Atk)
- Quiver Dance
- Bug Buzz
- Hurricane
- Fire Blast

On Dragonite, it seems that you're using a sweeper set, rather than the tank set, so Dragon Tail is out of place. Instead, use Roost for recovery, Brick Break to deal with Ferrothorn or other Steels, Draco Meteor for huge power or Aqua Tail/Surf for more benefit in the rain.

Nidoking seems out of place on a Rain team because its Water weakness is amplified there. Replace it with Ferrothorn or Scizor because their Fire weakness is reduced in the rain:

Ferrothorn:
-Spikes/Stealth Rock
-Leech Seed
-Power Whip/Protect
-Gyro Ball/Protect/Thunder Wave
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers

Scizor:
-U-turn
-Bullet Punch
-Superpower
-Pursuit/Quick Attack
Nature: Adamant
EVs: 248 HP/252 Atk/8 Spe
Item: Choice Band
Ability: Technician

your team is extremely weak to opposing Starmies. A simple Life Orb+3 Attacks set 6-0s you if it wins the speed tie aganist your starmie. So like the post above me I would reccomend sticking a ferrothorn on your team over nidoking. Nidoking isn't really doing anything for the team besides demolishing stuff which you already have dragonite for. next on the list is Jirachi. It's sub CM set completely destroys your entire team after a single turn of set up which is really bad. Since you not only need a check to Jirachi, but also subtoxic gliscor I'm recommending you try out a SpD Bronzong. In rain Bronzong is nearly invincible and makes a solid check to a lot of things that are destroying your team. I'd say replace Toxicroak with it as he really isn't doing anything productive for this team.

Bronzong@ Leftovers
Levitate
Sassy
252 Hp | 252 SpD | 4 Def
-Stealth Rock
-Toxic
-Hidden Power[ice]
-Earthquake

With that you're no longer weak to dragons either who really had a fun time wrecking your team as well. The last thing I want to address is a few nitpicks. Fire Blast on Volcarona in the rain is really silly because rain ruins it, Ferrothorn and other steels you would be hitting it with are going to be hit hard by hurricane and bug buzz after a couple boosts. Try something like Hidden Power[water]. I know it sounds a little dumb but it effectively beats all the common volcarona checks, hurricane beats terrakion, dragons and gyarados while hidden power[water] means heatran can't do anything against you either. Next that Starmie set really isn't taking advantage of all Starmie has to offer. Since your team really needs spin to survive, I'd recommend replacing damp rock with Life Orb and then changing Rain Dance to Recover. This makes Starmie have a lot more staying power and it means you can spin more often. With that the team looks pretty good. Good Luck.