First Competitive team

Question

Please tell me how to make this better?

Tangrowth @ Occa Berry
Ability: Leaf Guard
EVs: 252 HP / 252 SpA / 4 SpD
Modest Nature
- Sunny Day
- Solar Beam
- Natural Gift
- Synthesis

Absol @ Chople Berry
Ability: Super Luck
EVs: 252 Atk / 252 Spe
Adamant Nature
- Swords Dance
- Night Slash
- Psycho Cut
- Iron Tail

Klefki @ Air Balloon
Ability: Prankster
EVs: 252 Def / 252 SpD
Bold Nature
- Reflect
- Light Screen
- Hidden Power [Grass]
- Spikes

Darmanitan @ Sitrus Berry
Ability: Sheer Force
EVs: 252 Atk / 128 Def / 128 SpD
Adamant Nature
- Belly Drum
- Hammer Arm
- Flare Blitz
- Hidden Power [Electric]

Goodra @ Assault Vest
Ability: Gooey
Shiny: Yes
EVs: 4 HP / 252 SpA / 252 Spe
Modest Nature
- Dragon Pulse
- Focus Blast
- Hidden Power [Fighting]
- Muddy Water

Golurk @ Spooky Plate
Ability: Iron Fist
EVs: 252 Atk / 128 Def / 128 SpD
Adamant Nature
- Iron Defense
- Shadow Punch
- Fire Punch
- Thunder Punch

Comments

This team could really use a Mega. I see Mega-Charizard Y good-fitting here over Darmanitan, for it brings Sun that Tangrowth likes, weakens Water-type attack that threaten a bit Golurk and empowers Fire Punch and Fire Blast which may come off as coverage moves in some of your Pokemon.
I don't get your items choice. You are using way too much berries. Frankly, that's no good.
Tangrowth can easily use Leftovers rather than Occa Berry. You should switch to Goodra for taking an eventual Fire-type attack anyway. Absol and Golurk like the extra power Life Orb can offer to them. Goodra appreciates the extra bulk an Assault Vest can grant it. Klefki, while Air Balloon is good, would also fancy Light Clay so that screens stay for longer.

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Concerning the movesets, some quick suggestions:

Tangrowth: Ditch Natural Gift and replace it with Infestation. If you're going to have Sun support from Prankster Klefki and Megazard Y, then you may as well use Leech Seed > Sunny Day for added passive damage and recovery.
Absol: Go mixed. Absol's frail and can't really set up because of its lackluster speed. Try something like Fire Blast, Sucker Punch, Superpower and Night Slash / Pursuit. Pursuit can be used to trap to death any Pokemon that takes supereffective damage from it, depending on your own predictions.
Klefki: Hidden Power Grass should be replaced by Toxic/Thunder Wave to cripple your opponent's team.

Charizard @ Charizardite Y
Ability: Blaze
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Fire Blast
- Solar Beam
- Focus Blast
- Roost

Try this Charizard to replace Darmanitan.

Goodra: Try Fire Blast somewhere. And replace Hidden Power Fighting with Focus Blast; accuracy is a necessary evil for Power matter more generally, especially early-game where you can afford to miss once or twice.

Golurk: Use Stealth Rock > Iron Defense to provide more utility and to deal passive, cheap damage to newcomers. Use Earthquake as well instead of Thunder Punch.

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like RecreatedReshiram said, you need a mega. if you don't like Charizard Y, as Darmanitan is physical, and Mega Zard is special, try mega Blaziken. Life Orb over Spooky Plate on Golurk. you only have Spikes for set-up, get Stealth Rock (mabye Skarmory).  i would choose a Razor Claw or Choice Scarf on Absol, as Absol is to much of a glass cannon for Chople Berry to be very helpful. Also, a Rapid Spinner is helpful to deal with Stealth Rock. if you want a Fire type Natural Gift, use Watmel Berry for more power, or ditch it entirely for Toxic and Leftovers. No pokemon on your team has Earthquake, a big help on any team. put it on Golurk, as he gets STAB boost from it, and get rid of Fire Punch, as Thunder Punch covers his Water weakness, and Grass isn't that common (on less than 50% of teams).

I am still a bit of a noob, so some of suggestions might not make sense, but give them a try anyway.

Hope I helped