Although this is written from a cosplay/convention point of view, many of the points are broad enough to really apply to any costuming situation.
- Know and like the character you are portraying.
Specifically, don’t be bullied by friends to round out their big group cosplay if you don’t like the character. Costuming tends towards being large money- and time-sink, and why would you spend the effort on something you don’t love?
- Be physically comfortable in your outfit.
This includes: the coverage (or lack thereof), the types of garments you are wearing, shoes, large extruding parts or heavy weights, wearing a wig/intricate hairstyling, mobility restriction, weather condition preparedness, and knowing the amount of time you can handle standing around in the outfit.
- Be emotionally comfortable in your outfit.
Part of emotional comfort is handling the large numbers of people, some from the venue and some not, who are going to see you (and looking at you quite closely) in your outfit.
The other part of emotional comfort has to do with the pieces of a costume and your personal feelings about them. Say, if the outfit has a cross motif and you’re not Christian (or you are Christian and feel uncomfortable wearing crosses outside of religious contexts); the ideological context of the symbolic or culturally-linked articles of your costume. Think about what your personal feelings will be when you wear the outfit.
- Stay in your budget.
That means make a budget. Yes, it might be a bit anxiety-inducing if you’re wondering whether you’ll be able to squeeze five more yards of casa satin out of your last $20, but that’s not nearly as bad as buying all costuming supplies and having no food money for two weeks.
- Give yourself enough time.
I have never known a costumer who complained that they gave themselves too much time to make a costume. Give yourself time to hunt for sales, time to do everything ‘properly’ (like pressing each and every seam), time to throw the whole thing at the wall and pout for a few days when you’re frustrated. Buffer time is especially important when something crucial to the costume requires a new or difficult skill.
Crazy deadlines tend to be bad for stress levels, even when your only obligations are eating and sleeping. It’s even worse when classes and/or jobs have to be factored in.
- Don’t plan on extreme measurement changes.
Making a costume 2 sizes off from what you wear, in the hopes you’ll be 40 lbs heavier/lighter in four months is a terrible. Also, you’ll be a sad panda when your lovingly made costume doesn’t fit.
(being pregnant is an obvious exception to this)
- Have pockets.
Pockets are awesome; when your phone and wallet are physically attached to you, you don’t need to worry so much about losing them.
- Finish the outfit. Completely.
Using safety pins to hold your costume closed will not boost your confidence in it.
- Inspect before wearing.
Just to make sure everything looks the way you want it. If possible, have a friend check you over for anything out of order.
- Clean after wearing.
Also, store the costume properly, so it will be ready for next time.