Detail can refer to anything from proper sizing to straight stitching. The detail work, making sure that it fits properly and hangs just right, is the correct color...etc. sets apart a good costume from a mediocre.
Here are some details that you can perfect to make your costume great.
1. Colors - I can't stress that enough. If you start off with a fabric color that is 'close' but not quite right, it will be downhill from there. Nothing to me is more painful than seeing a beautifully constructed costume, only the base color is wrong!
2. Fabric Choice - I know Walmart sells cheap solids, but if your character is clearly decked in a satin or something heavier, don't skimp! Use coupons or whatever you can to ensure your fabric has the right look and feel for the job. The opposite problem persists too; some cosplayers like to make everything out of shiny fabrics. Most characters costumes don't look like they would have a sheen, so don't give them one!
3. Sizing - So, you couldn't find a pattern for that Sailor Moon costume, and you tried some free handing. Probably started it big just in case, and figured you could cut it down to size. Only problem? Sizing is a nightmare. Get a friend to help with difficult to pin areas, and make sure your costume isn't baggy (unless it's supposed to be!)
4. Detail to Scale - I just did a costume that has buttons on it, and in every cosplay photo I have seen, cosplayers used real buttons that often times didn't match and in every case were TOO SMALL! Use your reference photos to figure out how large (it's anime, so everything is big except for the skirts) your detail items should be.
5. Make it Match - The above example suits this perfectly. I didn't buy buttons. I made them from the same material used for the trim work. Likewise, I found pink tights but they were the wrong color, so I got Rit Dye Remover and faded them until they were. This is such a small thing, but it makes a difference. If I'd left them people who see the costume would say "oh, she did a nice job, but the tights didn't match."
Happy Cosplaying!
