Using Omen of Pestilence near a turret, when no enemy champions or minions are nearby, will cause the ghoul to attack the turret. This can increase Yorick's pushing power as it will deal 35% of Yorick's attack damage to the turret and increase his damage output by 5% while the ghoul is alive.
Be careful when using his abilities near towers, as the ghouls auto-chase and attack nearby champions, causing unintentional tower-aggro.
Allies can Teleport to your ghouls. This can help set up ganks.
Yorick is an exceptional solo laner. He can use his ghouls for zoning as a deterrent against enemy champs to keep them from last-hitting minions and to keep them out of experience range. His ghouls also allow him to gain minion kills and experience without having to put himself in immediate danger.
Alternatively, Yorick can jungle as his ghouls add significantly to his damage output and damage resistance.
Omen of Famine has the highest mana cost and lowest damage output of Champion abilities and thus is best used only when regaining health and survivability are priority and when mana is not low.
This also makes Yorick a great sustainer in lane allowing him to be able to force the enemy laner to recall while Yorick is able to stay in lane with his Omen of Famine.
With good timing, Omen of Death grants you an additional temporary ally as well as giving one of your allies a brief life after death. This is because the re-animation effect gives full health even if the revenant is near death.
By targeting one of your high damage dealers or the carry, you can turn a fight into a 6v5.
If you ult your carry and the enemy takes them down, then the carry is given a second opportunity to destroy the enemies.
If you ult an ally that is channeling an ability, and they die while under the effects of Omen of Death, they will continue to channel that ability, too.
On the other hand, targeting a tank will provide a good meat shield to take tower hits.
A Manamune offers a lot of flat mana and converts it into attack damage. If you do not need more defensive power early on, this Item can work very well.
Yorick mana problems do not weaken late game, staying out of your base for a long time will consume your mana quickly, instead, keeping Manamune will allow its evolution to Muramana offering even more attack damage and a powerful active, allowing you and Omen of Famine to hit very hard.
A Chalice of Harmony leaves you with a lot more money than a Manamune, allowing you to pick up Items according to your situation earlier. By itself, Chalice of Harmony already gives a bit of magic resistance, so it works especially well against magic damage. The disadvantages are that it doesn't allow you to spam ghouls quite as much as with Manamune and you have to sell it at some point, thus losing a bit of gold. Chalice of Harmony can now be upgraded to Athene's Unholy Grail, giving more magic resist, mana regen, returning mana upon kills/assists, as well as adding ability power, (which makes Omen of Pestilence hit very hard) and some cooldown reduction. This item is better used if you enjoy constant ability casts, as it provides CDR that Manamune lacks and allows much devastating harassment with Omen of Pestilence
Glacial Shroud is a good item for early mana too. The armor increases your survivability and the cooldown reduction increases your damage. This option requires you to conserve your mana yet it doesn't lose value nor has to be sold.
A popular trend among Yorick players, is to load Yorick with tons of offensive masteries and build tank mana items early on, stacking armor or magic resist depending on their lane opponent, then going back on offense items after getting a few core defense items, foregoing Manamune and instead focusing on improving lane sustainability, damage trading, and tower diving capability.
Sheen, or Trinity Force have great synergy with Yorick, as well as giving him much needed stats. Iceborn Gauntlet is also great item for Yorick (arguably better than Trinity Force), as it provides the spellblade buff, armor, mana, and cooldown reduction, which all are essential on Yorick.
Getting at least some crit chance is a good idea, as the 5% bonus damage per ghoul from Unholy Covenant applies to the critical strike damage as well.
Take a great care when engaging Yorick 1v1. His 1v1 capabilities are high due to his ghouls. Since they make for most of Yorick's damage, a champion that can destroy them instantly is an excellent option against Yorick.
Master Yi can use Alpha Strike to instantly destroy the ghouls when they are summoned. Also, he himself has a heal, and thanks to his build path, Master Yi is one of the few champions on the game who can match Yorick's dueling potential.
Volibear can use Majestic Roar to fear Yorick's ghouls, and his passive gives him enough sustain to win duels against Yorick.
Although Malzahar has no health sustain, he can use Malefic Visions on the ghouls. Thanks to them losing health over time, it makes easier for Malefic Visions to pass to another ghoul. This makes Malzahar regain a lot of mana over them. Malzahar is also ranged, so it's harder for Yorick to harass him.
The active of Statikk Shiv can chain off Yorick’s ghouls, making their lifespan shorter, ergo reducing his tankiness.
If you are a melee champion, Ravenous Hydra's splash damage makes easy to kill Yorick's ghouls at same time. This item also provides sustain, although it may not be enough to compete with Yorick's sustain.
The amount of healing he receives from Omen of Famine depends mostly on the initial magic damage dealt by the spell. Buying magic resist can greatly reduce the heal Yorick gets from the spell.
When he uses his Omen of Death, consider killing the revenant first rather than the champion it mimics as the revenant is weaker than the original champion.
Be careful when a champ is revived by Omen of Death, they know they will die anyways so they will go all out to kill you, even tower dive, try to CC the revived champion until its duration is over
When being chased by his ghouls, you can avoid them like escaping from creeps, i.e. quickly run into the nearest brush then press S key to stop attacking.
Although Yorick's early game harass and sustain is potent, he is not naturally tanky. The fact that Yorick is forced to buy items that early game give him no tankyness at all, coupled with the fact he has no escapes, means that Yorick starts to lose effectiveness when the laning phase is over. He is also vulnerable to ganks, so calling for help will be the bane of Yorick.