To decrease your Life Points to below 1000 or 100 whenever possible.
To deal more than 10,000 damage when you have 0 cards left.
To get 5000 - 8000 score. Improve your score by using glossy and prismatic cards for additional assessment points.
1. Receive an attack to get Cerberus
To get Mythical Beast Cerberus from your deck, use either "Sorcery Conduit" or "Draw Sense: Low-Level". Both skills are similar and they require you to receive at least 1800 points. You can use cards like Enchanted Javelin for some protection. After taking 1800 damage, a button will show up during your draw phase if you want to use it.
Some Legendary Duelists often start with monsters that won't deal 1800 or more damage, if you have cards that can reduce your LP like Abyssal Designator on your first turn, you can use it to ensure that you can activate the skill next turn.
Even if you have Cerberus in your starting hand, take the first hit if you want to adjust your Life Points to 100 to get the "LP on the Brink" assessment. Unless you use cards that can take you to 100 LP from 4000.
Recover your LP if you think you will take damage more than your current LP, use a Blue Medicine or any other healing card. The damage you take will still count towards the required damage for the skill to activate.
Use Enchanted Javelin to maintain 4000 LP and still be able to activate skill to draw a Cerberus.
Keep equip spells in your hand until you summon the Cerberus. You cannot activate Spell cards if your three spell zones are filled, but you can use a Gravity Axe - Grarl early to lock your opponents in defense position.
If your opponent has cards that can inflict effect damage to your Life Points, don't lower your LP early in the duel. Instead, use it on your last turn when you are left with 0 cards in your deck.
Combo By using Murmur of the Forest, you can re-use a field spell so you can activate it again for another counter to Cerberus. Alternatively, you can use Sword of Deep-Seated and twister it to re-use the effect.
3. Dealing the damage
When you have 0 cards left in your deck, and used up all your spells, you can attack your opponent by using Stop Defense on one of your opponent's defense card and then use Riryoku to increase Cerberus even further. Afterwards, equip Shooting Star Bow - Ceal on to that reduced monster's attack. If you used your stop defense earlier, then you can equip the Ceal bow to your Cerberus to be able to direct attack.
I don't quite understand why people don't use Mage Power on this deck. I run 2 x Mage Power on mine (I would run 3 but I need one spell/trap free for my prismatic Anti Magic Arrows) and Cerberus gets to ~12000 ATK easily, leaving place for traps, monsters, or to play spells without Cerberus on the field, maybe to counter the opposition. Am I missing something or is Mage Power underappreciated?