Not Updated For Current Season
Ghost is so you can chase a fleeing enemy or to run from certain death. (If you want to use Flash instead, thats good to. Makes it easy to turret dive an enemy with low health and Flash to safety.
Exhaust is good for turning a losing battle around or to catch that guy that's fleeing or even to escape if you need to. (*Warning* Be carefull when fighting Master Yi if he's using Highlander, you cannot slow him. If he's losing a battle and is fleeing, it's best to save Exhaust for another enemy unless highlander wore off before he started to flee.)
Leap Strike is first because you can get to battle fast and you can use it to flee if you need by targeting a friendly.
Empower is next because it's your heavy hitter and the cooldown is short. Spam it in battle and you'll own.
Counter Strike is your next skill you want to upgrade because of it's AoE stun and dodge chance. You can farm creeps, or if you're getting ganged... stun them and run.
I chose Greater Mark of Attack Speed and Greater Glyph of Attack Speed to help with Relentless Assault's and Guinsoo's Rageblade's passive abilities. The faster you can attack the more they'll get hit by that uber 3rd strike.
I obviously chose Greater Seal of Evasion and Greater Quintessence of Evasion for the added dodge. It'll help save you from alot of damage and get you Counter Strike easier.
Start off with Cloth Armor, 2 Health Potion, and 1 Mana Potion. The extra armor will help against harassment from other champions and against the creeps. The Health Potion and Mana Potion will help you lane longer and pick up the extra levels and gold you'll need for when you recall.
Ninja Tabi should be the first thing you pick up after you recall, and pick up Blasting Wand and focus on getting Guinsoo's Rageblade.
After you get Guinsoo's Rageblade pick up Stinger for the extra attack speed and focus on getting Nashor's Tooth next. It'll help your Relentless Assault's and Guinsoo's Rageblade's passive abilities and get those stacks faster.
Now that you have the attack speed from Nashor's Tooth, time to get some ability power. Grab Needlessly Large Rod and focus on getting Rabadon's Deathcap as soon as you can.
Now that you've gotten Rabadon's Deathcap out of the way you can pick up Sheen and work torwards Lich Bane, the passive will help alot when spamming Empower.
Grab Hextech Revolver and work on getting Hextech Gunblade. The life steal and spell vamp is indeed amazing, and the active can slow those enemy champions that try to flee your wrath.
If you're up against alot of magic users. (ie. Lux, Malzahar, Ryze, etc.)
I would work on getting Banshee's Veil for your third item instead of Rabadon's Deathcap, it gives 50 magic resistance and will block one negative spell every 45 seconds.
A lot of people like Quicksilver Sash, while it does get rid of all debuffs you got, the cooldown time is a nuisance. I would only recommend this item if they're focusing you during team fights.
I use Force of Nature a lot but that's only to prevent incoming magic damage, it doesn't stop stuns, snares, silence, etc. so I only recommend this when facing champions such as Akali, Amumu, Veigar, etc.
More to come...