Now, i want to make this clear, Schaco is quite a tricky character to play.This build will not make you start owning the game straight away, it takes practice, but this build will certainly help. I tried many different combinations but this one seems to be the the best of the lot.

Important fact: Shaco may have mad dps but never initiate a battle you ar an assasin. Stay near the back of the fight or in brush to maximise decieve effectiveness.

Pros

High attack damage
Crazy attack speed
Good at harrasing early game

Cons

Very squishy early game
takes a lot of time to master
very dependant on items.

Now the runes are fairly straightforward. Adding on Shacos attack damage with the Greater Mark of Strength and attack speed with the Greater Seal of Altricity while also increasing crit chance with Greater Glyph of Malice. Also adding helth quintessences to make Shaco a little less squishy early game. These help getting early kills.

First i always take dagger, just to give you that attack speed bonus but boots of speed work alright. After that get the Beserkers Greaves. Second i always go malady it gives 50% attack speed and also 25 AP. Next you can either go with the stinger or levathian. If you are being targeted and need a health boost go levathian, as it is a cheap way of getting lots of health. If not go stinger. The Trinity Force comes next because it is an all rounf great item, terriblt expensive but ive gives you a bit of everything, but most importantly makes Shaco less squishy. Nashors tooth is a must get because of its cooldown reduction, it also gives shaco even more AS and AP. Last but not least is the black cleaver which gives you a huge +75 attack damage and also the handy passive of reducing you targets armour.

First skill i always get is Two Shiv poison , it is a great move for harrasing champions early and getting them on to a low health, i max this first as it does quite good damage when levelled quickly. Decieve is a good move for taking a champion by syurprise or to escape quickly an easily. i max this second. I find Jack in the box quite a useless ability as they only last six secnds after firing so i dont get a point till i have to, but that is just my opinion. Hallcinate is a good move for one on one fighs it basically makes it a tqo on one, it also deals a lot of damage upon death.

Backstab: (Passive): Shaco deals 20% bonus damage when striking a unit from behind.

Decieve: (Active): Shaco instantly stealths for 3.5 seconds, teleporting to a target nearby location. If he attacks while stealthed, the attack is guaranteed to crit for bonus damage.

Jack in the Box: (Active): Shaco creates a Jack in the Box at the target location. It will Stealth after 2 seconds, and pop out when an enemy comes near, fearing nearby enemies for a few seconds and attacking them. It deals magic damage, and lasts 90 seconds stealthed or 5 seconds while firing. Casting Jack In The Box breaks stealth. Cannot be cast inside walls.

Tow Shiv Poison: (Passive): Shaco's attacks poison his target, reducing their movement speed for 2 seconds.
(Active): Deals half weapon damage plus extra damage to target enemy, and poisons them for 3 seconds. The passive is not in effect during the cooldown. Slow Works With Backstab.

Hallucinate: (Active): Shaco creates an illusion of himself nearby, which deals 25% less damage and receives 50% extra damage. This illusion deals half damage to towers and inhibitors. On death, the illusion explodes, dealing damage to nearby enemies. Lasts up to 18 seconds.

What to get:
Ignite: A must get, it helps cut down the enemies hp and is also habndy for finishing of fleeing enemies.
Exhaust: Good with Schaco as it can allow Shaco to get in range for his TSP ability that will slow them.
Ghost: an all round good spell that can be used to catch up or get away.

What not to get:
Flash: Just use decieve
Clarity: No need as Shaco mainl relies on basic attacks
Revive: Why would you need it?

To me this is the best way to play shaco, Attack speed and damage while also getting some items to improve his health. If you have evr played against a half decent Shaco you know how difficult they are. With this build, and a bit of practice you should be owning the fields of justice in no time at all.