Now Zac is a very tanky jungler, and is able to clear jungle very quickly with his unstable matter. When you start the jungle; start at the Wolfs (always get a leash for the first 2) then move your way over to the Blue Golem, when his health gets low enough smite him. Then move your way of to the wraiths (if wolfs are back up by then pick them up). After taking wraiths move to the golems, by the time that's all over you should be level 3 and have smite back up, which then you should go over to Red Lizard and pick up the red buff.
Ganking with Zac is easy with his Elastic Slingshot's range, however you have to remember that even though Zac is a tank he still can't 2v1, always make sure you let your team know when ganking so they can set up an easy Slingshot and they can easily pick up a kill or an assist.
Let's take a quick look at Zac's abilities;

Stretching Strike - Zac lashes out with an elastic punch, dealing 70 / 110 / 150 / 190 / 220 (+ 50% AP) magic damage to all enemies hit and slowing them for 20 / 25 / 30 / 35 / 40% 2 seconds. This move has a really good range and can pack on some damage late game. The slow also allows teammates to either catch up or get away. When chasing an opponent the boot's you've built will give you speed advantage and allow you to be able to catch up and slow (pretty basic).
Unstable Matter - Zac's body erupts, dealing 40/55/70/85/100 Magic Damage +4/5/6/7/8 (+0.02)% of the enemy's maximum Health as Magic Damage to all nearby enemies (Max: 200 damage against minions and monsters). This ability allows you to clear jungle very fast, that's why it's the first one maxed. When in lane you are able to catch up Stretching Strike followed by a Unstable Matter to deal tons of quick damage.
Elastic Stringshot - Charges up and launches towards a target area, knocking up enemies.
Zac faces the cursor and charges up over 0.9/1/1.1/1.2/1.3 seconds. Reactivating the ability launches him towards his target, dealing 80/130/180/230/280 (+0.7) Magic Damage to all enemies hit and knocking them back for 0.5 seconds. Finishing this move last allows you to be able to get bigger damage and better jungle sweeps. However when building picking up another point at level 8 is good for when ganking you are able to quickly distort the other player with a bounce and then only a short time later you can do again instead of chasing them down risking a turret dive.
Let's Bounce! - Zac bounces 4 times, knocking up and slowing enemies.
Each bounce deals 160/240/320 (+0.25) Magic Damage to nearby enemies, knocks them up for 1 second, and slows them by 20% for 1 second. Enemies hit more than once take half damage and are not knocked up. Zac gains an accelerating movement speed buff (20-50%) and reduces the duration of stuns, slows, taunts, fears, silences, blinds and immobilizes by 75% while active. This move allows for great crowd control during team fights; when in team fights you'll want to Elastic Stringshot, then quickly follow up with a Let's Bounce allowing for a lot of opponent down time during the battle. Let's Bounce! is also a great way of getting way from a gank or great for going in for a gank and catching up to people running away because of it's speed boost. Another great thing about Let's Bounce! is that you can use Unstable Matter while using it which can come in handy once in a while.
Cell Division - Each time Zac hits an enemy with an ability, he sheds a chunk of himself that can be reabsorbed to restore Health. Upon taking fatal damage, Zac splits into 4 bloblets that attempt to recombine. If any bloblets remain after 8 seconds, he will revive with an amount of Health depending on the Health of the surviving bloblets. Each bloblet has a percentage of Zac's maximum Health, Armor and Magic Resistance. This ability has a 5 minute cooldown. It's nice to have a backup when taking fatal damage, you are able to Cell Divide either coming back to life or taking up opponents time having to kill you, giving your team precious time to get away.

Now this is my first guide, so I'm aware it's a little blah, but I've been working with Zac since the day he was released, and looking deep into him before. So this guide does work well, it's just a little...blah.