So you've built a costume, possibly by sewing a costume from scratch, modifying existing items, or building one out of EVA foam/Worbla. But there's still more to help a costume feel complete! There's props, makeup, wigs, and if it's something you want to do, taking photos. This page covers some tips and resources to help your costume (and you) really shine.
Part of cosplay is looking like the character you've made your costume after, and that tends to involve some makeup. Even for characters that look almost exactly like you, you might want to consider wearing makeup to even out skintone and make sure your features show up well in photos. More advanced techniques involve using makeup to change how the shape of your face looks (like more masculine or feminine, or shorter/rounder) and make your eyes look larger or smaller.
While we're on the topic though, something very important to remember: you do not need to be the same height, weight, body shape, or gender to cosplay a character. If a character is a race other than yours, do not under any circumstances change/darken your skintone (sometimes called racefacing). If you feel uncomfortable cosplaying someone from another race, consider creating an alternate version of them that you would feel more comfortable dressing as, or choosing another character from the series. Cosplay is and should be for everyone, and that includes being aware of real-world cultural issues. However, if a character has skin color outside of what appears in the real world (green, blue, pink) and is otherwise not coded visually as a real culture or race (consider their hair texture, for example) then feel free! Body paint is a fun challenge, as is learning how to make arm socks.
More than likely, you will get asked for photos while in cosplay. You can of course always say no, but if you want to have pictures taken (and especially if you decide to do a photoshoot with a professional photographer) it's a good idea to have poses in mind, and have practiced them ahead of time. Yes, practice! You'd be surprised how easy it is to forget even the most basic poses.
So you've got makeup on, you've learned your pose, and you've even taken a few pictures. What's left?? Well, does your character have a distinctive item associated with them? It might be a good idea to make that, which will make you more recognizable in the con hallways and give you something else to use in photos.