Level 2 - After safely generating 3-4 graves you look to all in the enemy by hitting e then using q to raise mist walkers so that your wave dosnt push for no reason.
Level 3 - At level 3 you can look to do the same thing as level 2, setting up 3-4 graves using e on the enemy then activating q for the mist walkers.
Level 4 - Level 4 creates many opportunities because you have 2 points in q allowing for a lot more damage and with this damage you can start trading again.
Level 6 - Similar to pre 6 yorick you should e the enemy then ult rather than setting up your graves, after reaching range of the enemy put Dark Procession around the enemy caging them and finish them off by auto attacking and weaving in q's to auto reset.
Level 9 - similar to level 6 yorick can look to trade with the enemy just like at level 6, but if you have taken the first tower already then clear jungle and go back to lane when the minion wave is about to crash your turret.
Level 11 - at this point in the game you should look to join team fights, as fights around this time could decide the game. Depending on the situation of the game you can send Eulogy of the Isles to side lanes to split push if you are wining, but if you are losing its better to have yoricks wife fight with him.
Level 16 - same thing as level 11, exept use yoricks ult for team fights most of the time.

Yorick through levels 1 - 3 are really easy to play as you have so much lane pressure because of yorick being a lane bully. Because people dont often see too many yoricks, this can be very beneficial for you. During the early levels yorick can output alot of damage and becuase people dont know this you can play safe and last hit with q to set up for a all in at level 2 or 3 (refer to yorick power spikes on what to do for the rest of laning phase, mid game, and late game.)

Hold out on recasting q because rasing graves create mist walkers that shove your wave for no reason and give the enemy free gold to farm, both under tower because of the pushed wave, and from mist walkers.

Pre team fight engage
R-E-W-Q-AA-AA-AA-Q

Laning phase combo
E-Q2-AA-AA-AA-AA-Q

Laning phase combos continued
E-Q2-W-Q-AA-AA-AA-Q

All in combo while spit pushing (have ult up while split puhsing)
E-W-Q-AA-AA-AA-Q