First of all you need lvl 91 slayer and a hellhound task to be able to attack it.

Cerberus lvl 318 and has a max hit of 23
Requirement for fast trips are lvl 70 or 80 agility to save time travelling through the dungeon
Attack 85+ Attack
Strength 70+ Strength (85+ recommended)
Defence 85+ Defence
Ranged 75+ Ranged
Prayer 70+ Prayer (Piety, 74+ Rigour)

To get there teleport to Taverly Dungeon with the wizard

Follow the Red Path if no agility lvl to use shorcuts on maps

Attack Styles

Cerberus attacks with all three forms of combat:

Melee - Cerberus bites the player. This attack will only be used if the player is standing within melee range.
Ranged - Cerberus stands on her hind legs and kicks out with her front legs, firing a translucent spiky ball.
Magic - Cerberus lowers her head and fires a smooth black ball.
All of these attacks can deal up to 23 damage, and can be prayed against to nullify all damage.

Cerberus Summons 3 souls when hp is under 400
Red is melee
Blue is magic
Green is ranged

This sould deals 30 dmg if not protected with the correct prayer and drains 30 prayer points regardless you pray correctly
so its recommended to have over 60 prayer when the souls come out.

With the runelit plug it will show you the order in which you need to pray

Using a Spectral Spirit Shield will reduce the dmg to 22 and halve prayer drain from souls to 15 only.

Cerberus also spit 3 lava pools when he does de GRRRRRRRRRRRRR animation.
its easy to evade just move the opposite side and you wont take dmg.

Its recommended to pray Protect from Magic at all times
You can Melee Cerberus or Range it making you only tanking range and mage hits from Cerberus

The next gear setup is to equip the best in slot you have.

Melee setup

Range Setup

This is the table drop rate from Cerberus

Inventory to take
Sharks or better food

Good luck and have fun Grinding ur Crystals.