Congratulations! You've found a convention in your area!
You've looked at the website, you've googled for pictures. You know what you're getting into.
Now, you've found the place, so work from there.
Do you want to go alone, with a group, or in a pair? Should you drive every night, or get a hotel?
These are things to decide months before the con.
I've gone to my favorite local con for years now, and let me tell you, organizing a group is a pain. Does everyone have their cosplay? Is everyone driving? Does everyone have their tickets?!
Yeah, it's stressful.
Make sure you bring basic things like your wallet and keys, obviously, and I recommend a bag of sorts. You can usually find one that goes with your cosplay; use that to your advantage.
After everything is done, all that's left is the con itself.
Congratulations, you're about to go to a convention.