Shaco is one of my favorite champions, able to start and escape about any situation.

Pros:
Shaco doesn't need flash (Not everyone uses flash but a lot of people do)
Can appear out of nowhere and start killing people
Two-Shiv can do massive damage when you are properly built
You will quickly level up by jungling
Jungling is very quick for Shaco

Cons:
Early game may be slow until you get to level 6 and have a couple items
Shaco is susceptible to ganks early game

Smite:
Smite deals 420 + (lvl x 25) True damage to a enemy minion, pet, neutral monster.

This will help early game, see Jungling section below

Ignite:
Ignites an enemy unit, dealing (50 + 20 × level) true damage over time to a single target and reduces the health regeneration and the healing effects received by 50%.

This is helpful when you start attacking people...
EX: Someone you are battling is there and you start fighting him, you can ignite him when he has one bar of health left.

Jungling should be fairly easy for Shaco, especially the first monster.

If you do not know how to jungle with Shaco, here's how to do it...

Before-hand, go to the nearby your Ancient Golem and place a ward (to prevent ganks)

Ancient Golem areas
That prevents and interventions and will leave you and escape plan.

To Jungle:
1. Get to the Golem early (you don't need Golem, but it is recommended because of its effect)
2. Start by placing 2-4 Jack in the Boxes right where the Golem would be located
3. Kill the Golem (With or without Smite)

After Golem: (Continue in same fashion except only place 1 Jack in the Box)
1. Kill the wolves as they will promote you to level 2 if you aren't already
2. Go kill the wraiths, they might cause a bit of damage but you can use your potions
3. Go to the Lizard Elder and kill it (By then, you should have Smite)
4. Finally, go kill the Regular Golems and finish the first part of the Jungle

Finishing Jungle: (Repeat the order of kills on the enemy side)

As for items here are my explanations:

Guardian Angel:
This is for trolling the enemy team, you can start rushing everywhere once you get this item. When you die, you revive and can either Deceive or continue fighting.

Boots of Mobility:
Literally the perfect boots for Shaco, the boots fit in perfectly with Deceive. Although Deceive is only 3.5 seconds long, the boots allow him to get faster almost instantly after his cover is blown.

Rabadon's Deathcap:
This is where you start getting OP (Over-powered), your Two-Shiv will start being able to do some real damage against your opponents. (I usually finish my games with my Rabadon's because the enemy team does not last long enough for my other items)

Lich Bane:
This shouldn't need an explanation but, this is going to go with Deceive. Lich Bane allows for some magic damage after you cast an ability (DECEIVE), so along with the automatic crit after the ability, you also get some magic damage too!!!

Nashor's Tooth:
This is just for some cooldown reduction. Along with a bit of ability power, this gives you some attack speed (for jungling) and some cooldown reduction (for spamming)

Deathfire Grasp:
This also gives you some cooldown reduction but also has some bigger ability power bonuses. Not much to say about its active because I never use it.

Rylai's Crystal Sceptor: (Can get at anytime after Rabadon's)
This is for the Jack in the Box. This is the best item for killing your oppenents if you decide to spam you Jack and the Boxes. In addition to fearing and doing damage to your opponents, the Jack and the Boxes will now slow them, and then you can kill them with your Two-Shiv.