Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
With this build sequence in my last three matches I have gone 10-0, 12-1, and 17-3. Once you get to full stacks with attack speed you have enough life steal to kill anyone in a 1v1 situation. Also In 2 of those matches listed I was triple teamed at level 18 and whipped out all 3 players without dieing causing the other team to forfeit. Jax gets so much attack speed that he is also amazing at turret killing. Give this build a try.
My strategy in a 3v3 is to solo the middle lane until about level 10. Then I go back and forth between jungling and minion killing until level 18. That is when I really start worrying about getting turrets and killing players on other team.