You must be either a part of the media, store that sells video games or a developer.
There are free tickets but you need to jump through several hoops to get them.

You don't need to be invited but there is a lot of really annoying verifications you need to do. (Check stub to prove you are from the said company, and the like. I started my own company but never did go anywhere with it because of various issues, but I was able to go E3 several times.

e3expo.com

Go there hit register, attendee and there is a FAQ that covers everything. (The FAQ is within an applet so usually posting the direct link will not work.)

Sorry Yoda, eventhough we were quoted on Halo 4 box cover. 

But you can still have fun here.

Did you see my pictures from the Meet and Greet 2 years ago for the Xbox One at the Microsoft Store in West Los Angeles?  It went litterly around the block, and then some.  It was huge. 

Plus, remember people sat out for Week and Week, even in the Rain to get tickets to the Star Wars prequils when they came out.  This town be crazy, in a fun way.

@Djevolve if you can get in and I do too we should me up! 

As people have said, the only guarantee is being involved in the industry as either Dev or press. But they do fill out the event with guests and walk-ins. However, obviously not cheep or guaranteed and you have to be in LA at the time. I'm saying this off the top of my head BTW, things may have changed.

for media conference,you have to be a media person

for e3 expo,you can go as it is

You don't

It's actually easy... I pretended to be press from Vgchartz when I went in 2012 (Technically I was at the time).

And then you have people who throw a quick "game" website together and say they're "press" too. You can bullshit your way quite easily to be honest. It does cost money though.

I still get junk mail from them reminding me to prepare for the next E3. Money talks my friend. As long as you're willing to pay you can do whatever the fuck you want.

Sounds good to me, I will update this thread if I do get in, However I don't have time to wait around a block for a day. Do they say the location days in advance or do they say it and you have to get there as soon as possible?

I don't know.  It's different every year.  This sounds like it will be one crazy line. 

But unlike what so other have said, the general public CAN NOT get entraince to E3 - it hasn't been that way for several years.  They just got too many people.