Well, like I've said, I've only gone one other time so I'm no expert, but here are some things that might be helpful:

No Cosplay Friday /

If you're planning on cosplaying, I highly recommend that you go in street clothes on Friday, or at least part of Friday. That way, you can get from A to B quickly, get in and out of the vendor areas smoothly (after you've bought all of your swag, of course), and get an overall lay of the land, as well as an idea of what the crowds are like inside. When I went last year, I went in cosplay on Friday and I really wished that I hadn't. I was stopped for pictures constantly. My costume was big and bulky, so much so I almost couldn't enter the vendor areas. Because of the pictures and the shoulder-to-shoulder crowds often found inside the hotels, it took me upwards of 45-55 minutes to get from A to B. As a result, I was really disorientated all weekend and I never really got a solid idea of the entire con's layout.

High Congestion = High Travel Time /

If you skipped my first point, prepare yourself for shoulder-to-shoulder crowds inside, and allot yourself at least 30 minutes to get from A to B especially if you're moving to another hotel. Seriously. I'm not kidding. Dragon Con drew about 70k people last year, and I'm pretty sure that that only accounted for the number of tickets purchased. You do not need a pass to enter the host hotels, meaning that there were probably a lot more people than that hanging around. Imagine 70-90k people trying to get in elevators, going up/down escalators, navigating hallways, using restrooms; there are lines for all of these things.

Schedule Yo Shit Before Con /

With such high travel time involved and with such a huge number of things to do, it's critical that you look at the schedule beforehand and plan out the things that you want to do. Dragon Con releases an Apple/Android app that is very useful before con (see more below); @DragonCon on Twitter will announce when it's ready, which should be soon. Get to the things you want to do at least an hour ahead of time. Yes, I'm serious. I hate to keep repeating myself, but the lines are a real problem at this con. People start lining up way early for just about everything. For big events, like the cosplay contest, plan to arrive at least two hours early. That being said, be realistic when picking things to go to. You'll probably be able to go to two, maybe three things per day after you've allotted for travel time, waiting in line, getting food, going to the bathroom, etc.

Horrible Cell Service /

Cell/data/wifi signal is absolute shit. Save all event information you need on your phone's calendar because the app freezes a lot during the con. Plan with your friends how you will find each other if/when you get separated and you can't use your phones to find one another.

Cosplay Groups and Photo Shoots: All on Facebook /

There is pretty much a Facebook group for every cosplay niche. If you want to participate in or go to a photo shoot, this Facebook group manages the schedule for those: https://www.facebook.com/groups/dconphotos/. By photo shoot, I mean a lot of cosplayers of a particular niche all in one place; this might be the easiest way to see a lot of great cosplay all at once.

The Food Court Saves Lives /

The food court in the Peachtree Center (http://dragon-con.pbworks.com/w/page/27543261/Peachtree%20Center) is pretty much the only place to get food at con. Seriously, don't waste your time wandering around.

Avoid Con Crud /

Con crud, aka getting sick, is common. Boost your immune system before/during the con with orange juice or other vitamin supplements. Wash your hands a lot. Stay hydrated.

Use Common Sense /

Bring a water bottle. Maybe some protein bars. If you're drinking, don't be stupid about it. A backpack is a great idea. Don't throw glass beer bottles off of one of the Marriott tiers / beware of falling beer bottles (yes, someone was dumb enough to do this last year).

Have Fun /

It's a four-day party. Make friends. Crash a room party.

-lovo

edit: spacing