Garen vs Tryndamere

Trade with Decisive Strike (Q), then Judgment (E), and back off: the Decisive Strike silence stops your opponent from answering with spells.

During Judgment (E), stay closer to your opponent than to their minions: the nearest enemy takes extra damage.

After a trade, back off until Perseverance (passive) kicks in: without recent damage taken, you regenerate part of your health every second.

Activate Courage (W) just before the bulk of the damage: you first gain a shield and tenacity, then a longer damage reduction.

Save Demacian Justice (R) to finish: its true damage grows with the target's missing health.

Avoid taking a trade when his Fury is high: with Battle Fury (passive), it raises his critical strike chance, and Bloodlust (Q) turns it into healing.

Hit him when he walks up to minions to farm: each last hit gives him Fury, which Bloodlust (Q) then turns into healing.

Against Mocking Shout (W), back off sideways rather than turning your back on him: the spell only slows enemies who are facing away from him.

Once he hits level 6, plan for what comes after Undying Rage (R): he can't die during the effect, so back off or hold any CC you have, and finish him when it ends.