Well I'm not going (obviously, since it's in America and I live in England ^^), but I've been to cons before and I suppose that they're all pretty much the same sort of thing anyway, in terms of what's available and what you can do and what to expect. I've only been to a couple myself, but I've learned a lot from just going to them. xD
- Like Mariah said, bring lots of water. Lots and lots of it. Especially since it's in summer, you're going to be boiling hot. It can be pretty cramped in some convention centers which means it gets hot easily, also if you're going to wear cosplay, 99.9% of the time you will feel very hot whilst wearing that, so just bring along water to keep you cool and hydrated, and maybe one of those small, pocket fans.
- Bring your own lunch, too! I went to a con before and there really was not much available in terms of food.
Since I am quite a fussy eater, I didn't have much choice, and of course, because so many other people are there too, they're going to be queuing up to get food too, so you'll probably end up having to wait a while. Maybe it's different at Anime Expo, who knows? Maybe there are some restaurants nearby (maybe do some research on that before you go), but definitely just bring along some snacks because if you get hungry whilst walking around, at least you can have something to eat to give you plenty of energy.
- Get plenty of sleep the night before. Going to a con is a very, very busy day. You might have to leave early to travel, which will wear you out, and no doubt you will be walking around the majority of the day (so bring comfortable shoes to wear - if you're wearing cosplay, just bring along some spare shoes anyway so if they are hurting your feet, you can change into some more comfy shoes). Just make sure you have loads of energy: Don't do what my friend did, which was got NO sleep the night before, didn't bring any pack lunch or anything, so she ended up just fainting from exhaustion. x3 Convention centers can get really crowded and busy, so you need to make sure you have lots of energy because there may not be many places to sit down.
- If you are wearing cosplay, you might get people asking for your photo. Of course if you don't want your picture taken, don't be afraid to say no! If people continue to harass you, don't be afraid to talk to security. Unfortunately, I've heard a few stories of that happening before, but it is quite rare. However, there's nothing wrong in just giving you a heads up on it!
- Finally, when you go to a con, you may be very tempted to spend lots of money. Do not be afraid to bring a large amount of money, but remember to budget yourself, also don't try to bring too much in case somebody steals it. Don't bother taking a credit/debit card with you, the cash machines there always have loads of people queuing by it anyway. ;x
I hope these tips have helped you, it's always good to make sure you are well-prepared for your first con so it can be an enjoyable experience for you.
I'm sure you will have a great time.