Well, first off, let me say that I cannot give any advice on making costumes. ^_^; Some cosplayers may consider it a sin..but *whisper* I buy mine! *dun dun dun!* But hey, we all have our talents right? And sewing is not one of mine. What I can give advice on, is how to -care- for your costume or at least what I've found works. Please note this is all based on fabric-type costumes.
- Keep yourself clean. Showering regularly during the con will help keep your costume clean, or at the very least not smelling like sweat
- As fun as it may be, don't wear your costume 24/7, take it off for awhile, let it air out.
- When packing your bags, make room for a "cosplay-care kit" this can include things like Febreeze for fabrics, Spray on dewrinklers (Like Downy) and no-wash stain removers (like Tide to Go ) Please note that these products aren't all material friendly. Do a fabric test before spraying down the costume you worked 300 hours, or spent 300 dollars on
Other tips
-Whether you make or comission your costume, try to add a pocket or two somewhere on it, even if it's on the inside of the costume. This makes carrying things like cards, cellphones, money, etc a lot easier.
- Have fun! Strike a pose! Woot!
I understand most people already know about tips like this, but for a novice or first timer, maybe something will come in handy.