1. Where possible (i.e. if the costume dictates), use natural fabrics. Especially for anything remotely Medieval. Cotton, silk, linen, muslin, calico, sackcloth, wool. Your underarms/crotch will thank you at the end of the day.
2. Head straight to the upholstery department for any costume set either in outer space, an invented history, or before 1910. Dress fabrics in velvets, burnouts, brocades and other fancy finishes/weaves are $$$; the same thing designed for a curtain or a couch is probably a third of the price and twice as wide.
3. I hate stretch panne velvet.
4. HATE IT.
5. Don’t forget to age/weather your costume! (Again, if the costume dictates.)
6. Hand-dyeing your own fabrics will give you a nervous breakdown, but it’s worth it.
7. Don’t neglect your hair/wig and makeup unless you want to look like you’re in the final dress rehearsal of the school musical. A great costume means dick if from the neck up you look like you’re popping down to the shops. By the same token, great hair and makeup can lift an average costume.
8. Pockets! Sew pockets into everything! Pockets!! That handbag or backpack is not screen accurate! POCKETS!!
9. Don’t discount hand-sewing. You’ll get blisters and go blind but you can’t beat it for finicky work or anything that needs to look like it wasn’t made on a sewing machine because, for instance, they didn’t exist when your costume was worn on-screen/in print.
10. Your body-shape and size is completely immaterial and also fuck anyone who says you’re too short/tall/fat/thin/disabled or the “wrong” colour or gender to cosplay any character you damn well choose.