Wearing costumes at SF/F and Anime Conventions is something lots of people look forward to. Yet from what I've seen, a little forethought can help make the experience a lot more enjoyable for all!
1) If you tend to get cold easily, don't choose a skimpy costume. A lot of convention centers run the air on high to compensate for big crowds. This tends to make some of the rooms super cold. Nothing worse than being your favorite character yet you're curled up in a ball chattering through the weekend.
2) Inversely, if you tent to get hot easily, don't choose a heavy or multi-layered costume. What feels like a cold air-conditioned room to some people, to others feels warm or even hot. Dressing up in something you've spent a lot of time and/or money on and then sweating in it all day -- no fun.
3) If your sword/hammer/wings/antenna/other appendage is large, you'll need to avoid super crowded hallways or small rooms. The bigger the venue, the more this will be a concern. You'll also need to be aware of your surroundings more as your body now takes up more space than you're used to. You wouldn't believe the number of close calls I've seen between a costume and someone's face or eye. :P
4) Wigs are an extra layer and they tend to run hot. Hats tend to cause the same issue. Something to keep in mind.
5) If you're going to wear a mask or helmet, make sure you've worked in some ventilation and that you can breathe, and especially, that you can see!
6) Always, always plan ahead. And be aware that even when you're prepared, things can still go wrong.
7) Bring a sewing kit and extra costume parts in case of emergency. If something can go wrong it will.
8) Is your costume complex? Is it heavy? Make sure to bring a buddy to help! They can gauge if the zone if safe, steer you from trouble, and generally keep you upright.
9) If you wear a costume, expect that there will be people coming out of nowhere who'll stop you and ask to take your picture. The more awesome the costume, the less feet per minute you'll make while walking through the convention. Be ready.
10) No matter what - make sure to drink plenty of fluids and to EAT! Wearing costumes is work. Make sure to take care of yourself.
And above all else - have fun!
Have any costume tips? Please share! Any costume stories too. :)