I don't think of myself as a player with enough skill to teach others but, I'm getting tired of people saying how bad Yorick is. Ive heard several people in game mention he is the worse champ riot has ever released. Much of this stems from his new ability mechanic, which can take a bit to really get use to. While I agree that he may be a bit underpowered, I'm not here to complain about his downfalls. I just don't wanna hear "Please, don't pick Yorick!" every time I play. So, I'm making this to hopefully show him off as a more than viable champ.
I don't consider myself an authority on runes, items, or masteries. I'm just gonna talk about what I do when I play Yorick. Feel free to correct me or leave any kind of constructive criticism.

Greater Mark of DesolationX9 I like the armor pen. I tried strength, magic pen, and armor, but i keep coming back to the Armor penetration.

Greater Seal of Scaling Mana Regenerationx9 Yorick needs mana, badly. He can hog it pretty quickly, so I suggest you get some kind of Mana regen in your runes.

Greater Glyph of Magic Resistx9 You can't really go wrong with a good base MR in my opinion. Magic hurts ;)

Greater Quintessence of Healthx3 I like the extra health at the beginning of the game. Although, I'm sure you can swap these with whatever you feel comfortable with. I have even done well with swiftness.

0/21/9 I like this for early survivability and scaling. Also, The regen.

I was opening with Doran's Shield when I started playing Yorick. the stats are nice but I found myself languid and otherwise vulnerable to early ganks. Boots make me feel a bit more safe early on. I usually pick up a Health Potion and 2 Mana Potion. I could totally see 1 potion and a Sight Ward working just as well, if not better.

On my second trip back, I always pick up Tear of the Goddess and if I have enough, a Long Sword. The tear is great to have early, makes using mana much less tasking in your second laneing phase.

When I come back, I usually have enough to finish Manamune and Boots of Swiftness. Manamune, to me at least, feels like it is the perfect core item for Yorick. A must have in all of my games. Boots of Swiftness is just my preference. You could easily go for the CDR boot or mercs.

I get Sheen next. The damage is noticeable and of course, it builds into the Trinity Force. I don't usually like to use Trin force but I seem to excel with it on Yorick. The speed is really great on Yorick.

Spirit Visage is great on Yorick. I love the MR+CDR and the regen factor, awesome.

next, I like to get some more CDR Glacial Shroud first. Farm a bit and upgrade that baby to a Frozen Heart. You got that great CDR along with a nice amount of armor/mana and a kick *** passive.

here, I was a bit confused what to purchase next, but I have gotten use to Atma's Impaler it's pretty expensive but late game is great for your crits and the passive is neat.

Last but not least, I usually cap with a Tiamat Awesome regen, which Yorick loves. Also, you get a good amount of attack dmg and an interesting passive.

I'm sure their are tons of Combos on Yorick, thats just how I like to play him.

Yorick's Skilling is very situational. Depending on who your laneing against, your priorities should change.

I always open with Omen of Pestilence. Its does a decent amount of dmg and slowing. I always find myself focusing Omen of Famine though. You can stay in lane forever if you use it correctly. it's also a great harassment against mages. Yorick's Q Omen of War is neat, it just requires you to strike a target beforehand. If you can hit with your Q after getting a good W off, your target should not get far(especially since you get the speed boost from omen of war).

Yoricks ultimate is called Omen of Death. It creates a ghost like image of target ally or yourself. Yorick can then control the ghost and use him in combat. Also, if the target ally that you cast the spell on dies while the ghost is up, the ghost will sacrifice its life and give your ally a chance to get revenge for a short time. I have had to tell people over and over that they are not alive, they are still dead. he can also cast his ultimate on himself, creating a copy and turning a 1v1 into a 2v1 for a few moments. The ghost dies easily but deals a commendable amount of dmg.

Generally, the combo I use is W,E,Q. I get my slower out there early and chase the target with my famine ghoul. If all goes well ill usually catch up to them and land my Q, which gives me a nice speed boost and another ghoul along with a hefty amount of dmg. By the time my Q is used I can usually cast W again and slow them further.

Ignite And Flash Are my spells of choice.

Ghost would work awesome as would Exhaust

I don't think Clarity is necessary with all the mana regen you have latter.

Cleanse or Heal Would work fine too. It's all about preference.

I like Yorick, I hope you guys learn to like him too. he takes some time to get use to but hes worth it. I just find him to be a lot of fun.