Not to sound like a fanboy, but I've been using Stonewall008's build, and it works wonders:
Flat AD marks, believe it or not it's faster on Xin to have flat AD over AS, but if you have AS marks they'll work too, Flat Armor Seals, any Glyphs, I prefer MR/level cause it helps lategame, but some take Mp/5/level, that's fine too, and finally ArPen Quints.
Skill Q/W/Q, then R>E>W>Q for ganking/midgame. Early W levels let you Q more often, give more healing, and do more than barely leveling your E in the jungle, but E is stronger than W in the ganking/midgame, so level it up then. Q only gets slightly more damage, and it's CD doesn't reduce with levels, so it's easily the last to level up.
Smite/Ghost for spells, and this build lets you choose where to start. You can either start at golems for a slower and safer pace, or go the stronger/faster pace of starting at the wolf camp, killing only the Giant wolf, then moving to the Ancient Golem, killing it, then wiping the rest of the jungle out save Red. Blue pill, kill the 3 newly respawned camps, then Red, then gank to your heart's content.
Oh, and since I forgot to mention it, like almost all junglers, starting items are Cloth Armor and 5 Health Potions.