My tips on building and playing Jinx! I hope it helps you become a pro with her. :D

Pros

Epic ult that can be used to destroy an enemy any distance away
Natural attack speed
Slow and a bind
With Baron have fun hitting 1k+ over and over and over

Cons

Super squishy
Can be hard to land skill shots
Minions block

Zap!


Over all Jinx has more pros than cons in my opinion.

Alright as I said in the Pros and Cons Jinx is a very squishy champion though out the whole game. So when it comes to your team make sure you have a tank around you most the time. It is helpful if you have a tanky support, but if you don't once the lane phase is over be sure to stay close. If you don't you can be easily picked off by the other teams top, mid, ect. If you are okay with only 55% crit then build a Guardian Angel, but to me 55% is not acceptable! You don't need any armour if you just stay with the tank, that's his job!

In the lane phase try and get who ever is supporting you to be a tank, such as Taric or Volibear. This will be a great help as you are not Gangplank with highest base health. :P When making exchanges in lane help out your support with stunning the enemy with your Flame Chompers! What I like to do if wait for my support to stun them and as soon as they do I throw out my Flame Chompers! for a quick double stun.

In a team fight don't get ahead of your team and Leeroy Jenkins it. You need to stay in the back and focus the enemy adc, once they are dead and gone start taking out their main carries. Before the fight be sure to poke a bit with Zap! for it as a long range and is an easy poke.
This part is important, your ult. Your ult is a game changer! A wrong timed ult will cost you the fight, so don't screw up! You need to it in a way to hit as many enemy champions as possible. In a team fight make sure to hit them all when they are at least half health, the less health they have the better. Your ult works great with champions like Sona, Orianna, and Amumu. Their ults all stun/bring them all together. When this happens its your time to strike with a fear-sum Super Mega Death Rocket!

Alright we all (I hope) know how to farm so this on will be short. When farming use your mini-gun to last hit and use Fishbones, the Rocket Launcher to hit groups of minions. I dont use Fishbones, the Rocket Launcher until I have some crit, otherwise it just uses to much mana. Remember to focus on farming! Don't get carried away with harassing the enemy adc! FARM IS IMPORTANT!!!

I am not finished with this guide!