I prefer 3v3s over 5's because you are 33% of your team. I like that I matter more towards the whole equation of the match. Wins and losses weigh heavier on your shoulders with fewer excuses.

Jax fits the 3v3 lifestyle to a tee.

You can tend to make a bit more money in 3's, making the players that have million dollar items more viable.
Jax has a great balance of attack and defense.
He is well suited for 1v1 or 1v2's which happen a lot more in 3's.
Jax has quite a few item build options that can be tailored better in a 3v3.

Okay.. onto the guide.
I'm going to start with masteries because I know there is pretty much one school of thought for Jax. Most people get to Nimbleness then go full offense. While I like this build for 5's or arranged 3's, I think there is a better way for 3v3 pickup games.

I am almost always paired up with 2 other dps when I do autoteam 3's. So I run defense in my masteries to try to get a little survivability on our team. Now I'm not trying to turn Jax into a tank, as you can see from my item order. I just like a bit more chance to stay alive so I can get to these items.

Well I'm sure you can figure out my Defense tree, I bet you've got a question about the Offense side. I put 2 points in Alacrity for 2% attack speed just for a little bonus which I think is important for jungling. I've got 3 points in Sorcery for a 2.25% cooldown reduction. I think cooldown is more important for Jax, moreso than attack speed (especially for Counter Strike.)

Nothing new here:

Armor Pen for Marks Greater Mark of Desolation
Dodge for Seals Greater Seal of Evasion
Magic Resist for Glyphs Greater Glyph of Magic Resist


For a bit more early game help, Greater Mark of Health can certainly be used.
Obviously, dodge is a must for Seals.
And the Glyphs, I'm a bit torn between Cooldown reduction and Magic Resist. Either way is good.

Okay, now the bread and butter.

Game Start:
I go with Boots for my first purchase with 2x Health Potion

Early Game:
I usually don't go back until I can buy the Ninja Tabi and the Vampiric Scepter in one shot. I like the lifesteal in the beginning for longer laning after I've used up my health pots and also to aid in jungling.

Now, on my way to Guinsoo's Rageblade I get the Pickaxe first. I'd say either way is good, but I think this way is better for getting the buffs. By level 8 or 9, I'm soloing the dragon and picking up the other buffs in the jungle.

Mid Game:
Once I've picked up the Guinsoo's Rageblade its time to think about destroying other players. So I like to take the Zeal next. Added attack speed is great for my Guinsoo's Rageblade stacks and the run speed is clutch for ganking and escaping. Now I always get Zeal before the Bilgewater Cutlass because I like to have that run speed first to keep up after I've slowed them with the Bilgewater Cutlass.

Now for the next purchase, I either finish my Phantom Dancer or start my Banshee's Veil. If there is no real tank on my team or its a full magic team, I'll go with the Banshee's Veil

Late Game:
Once I complete my Phantom Dancer its normally time for a bit of defense. I am attacking rediculously fast and I've got a Exhaust and the Bilgewater Cutlass for slowing moves. I don't usually have any problem destroying people's lives at this point. My biggest problem at this point is usually survivability. Those magic users are pretty nasty and a Banshee's Veil is a great fit. If its all physical damage, I may go for Thornmail but that doesn't happen too often.

Now that I'm a little better at staying alive, I complete the Hextech Gunblade and if the game lasts long enough I'll get the Phage on my way to the Trinity Force or the Frozen Mallet At this point, it doesn't usually matter. Game Over.

In a 3v3 pickup game, I try to take the top lane. Jax is well suited for a 1 on 1 lane push. Combining his 3 abilities works great to take about 20% of the other guy's health away. A couple of those and he's on his way back to base.

The biggest problem with public games is that people don't call MIA's fast enough. So: PAY ATTENTION!! If you lose track of the enemies at the bottom, go up to the top jungle and pick up some money and XP there. Your lifesteal will help you keep killing even when you're being set up.

It's all about getting that money. Use whatever it takes to get last hits early in the game. Leap Strike in to a minion near the enemy hero. You will get the last hit on the minion and force the enemy champion back. He will think you're attacking him, but you are just racking up the cash. Don't stop getting money. Jungle when you feel heat on your lane, lane when you've got accountability of your enemies.

There are going to be plenty of opportunies to kill enemy players, don't force it. Only go for the kill when it looks like you can trap them. I try not to attack before I have a charge on Counter Strike. Then Empower and Leap Strike in there. Nail 'em, stun 'em, Exhaust, Bilgewater Cutlass, dead.

Although, don't use Leap Strike as an opener if you don't need to. Just walk in there and start it melee style. If you save this ability, you can use it later to either catch up to him or run away yourself. Remember that you can use it to jump to friendlies too.

Solo Dragon at level 9 and everytime he's up afterwards.

A buff you have is one the other team doesn't. Get those buffs!

Get a charge on Counter Strike before starting a fight.

Money, Money, Money

If there are MIA's, jungle.

If you're playing against another Jax, get Sword of the Divine after your Guinsoo's Rageblade I can't believe how many people don't get this against me.

Sometimes the item purchases need to be modified depending on the other team. Learn the specialty weapons with actives. Sword of the Divine Executioner's Calling Youmuu's Ghostblade and others should always be options.