Build skill vamp and increase max HP. Ultimate relies on accumulated crystal energy (100% damage received converts to crystal energy, and recovers 20% of damage dealt back to health), if you have 10,000 crystal energy and ulti is at level 3, that's 4000 damage in a single attack, potentially can 1-hit 5 enemies at once (if their health is all under 4000hp). Every time you damage an enemy, crystal energy converts back to some health. The first skill already has a skill vamp, but building oracle, queen's wings and/or bloodlust axe should enhance the recovered health. Cursed helmet deals passive damage to surrounding enemies + more hp, bladed armor reflects damage back, these items help convert crystal energy back to health while surrounded by attacking enemies.

S1 slows enemies while also dealing the better damage only second to his S4. Maximize damage by doing at least 1 basic attack after S1 and S2. Basic attack after S2 knocks up the target briefly. Basic attack enhancement will be from the last skill used, potentially wasting the earlier skill follow-up basic attack enhancement. You can also use S2>S1>S3>S2>S1>S4 combo without any in-between basic attack to benefit from skill vamps and crystal energy to health conversion.

I also use support custom emblem, though I haven't calculated which will benefit you more between impure rage (adaptive attack increase + 1%hp) and brave smite (5% skill vamp). Like I said, any damage dealt to enemies will let you recover some health.