I used to cosplay, but I haven't really been able to go to a con in a while, now... :< But I did for quite a while, and it's a LOT of fun! :3
Don't try to overthink or overstress about it. Go in, have fun, enjoy!
Make sure your costume is fitted correctly, so nothing'll slip down or fall off as you're moving about. Sometimes you may have to sacrifice a bit of 'authenticity' for stability. It's fine. People will understand. The longer you cosplay, you'll start picking up all sorts of little tips and tricks, here and there. :3 Part of the whole fun of cosplaying is making the costume.
Enjoy being greeted by character as you wander about the con. And if no one recognizes you, don't let it bother you. They might just have never seen the show/game/comic/whatever you're cosplaying from. Go for your
own enjoyment, of having fun in costume, and seeing everyone ELSE in cosplay, too. :3
If you're taking photos of anyone else, please remember to
ask first, if you can take their photo. Most people will say yes, but some may say no. It's usually nothing personal - they might be in a rush to get to another panel, meet up with friends and are running late. It's just basic Con Manners.
At the con, check with the info booth to see if there is a "cosplay repair" station. Those are very handy to have, in case of any cosplay malfunctions or breakages that may happen (and they can easily happen). If there is no cosplay repair station, it's good to have a 'first aid kit' yourself, back in your hotel room. Stuff like a needle + thread, glue stick/hot glue gun, tape... to do some quick repair work of your own. Also at the con info booth, check to see what photoshoots have been set up. You may find some of your favourite series in there!
If your costume is very complex or layered (or even if it isn't),
remember to stay hydrated. This is VERY important! Overheating and/or passing out is NO fun. So make note of where the water fountains are, and/or bring a refillable bottle with you.
Make sure you can sit down in your costume. Or at least can take a piece off easily enough so you can sit down. Wandering a con for hours can get very tiring, and you'll wanna sit down at some of the panels, and to eat, eventually! ;3
It's handy to have a special pocket, or pouch, sewn into your costume somewhere. If the character you're cosplaying doesn't have such things themselves, make yourself a secret little flap, or something, where you can sew in a pocket. And make sure it's firmly secured. It's a good, safe place to put stuff like your hotel key, money, and your phone.
I can't think of anything else at the moment, but those are the basics. Enjoy your first convention! Hope you have a blast!
