You need it.
I don’t care if you’re cosplaying a guy or if you are a guy, being in cosplay is akin to being on stage. Even if it’s just foundation and mascara, you’ll be thankful for it when you see pictures of yourself later on.
Wear some form of base.
I personally use Clean & Clear Finishes Mattifying Moisturizer. You only need a rather small amount and it works extremely well. Your makeup will last longer and it controls nasty shineface. You also need eyeshadow base to keep your eye makeup from creasing or smudging. I use Sephora Perfecting Eye Primer.
Don’t overdo it.
While being in cosplay is like being on stage, you are not actually on stage and everyone can see you up close. So dial it back a little. Tone down bright eyeshadow with neutrals, and go easy on the blush. And never, ever, ever, ever wear bright lipstick if you’re wearing a lot of eye makeup. A basic rule of makeup is balance. If you’re going big on the eyes, go easy on the lips, and vice versa. I cannot begin to tell you how many people do not know this, though.
In cosplay makeup, you really should play up your eyes, in which case you want to be wearing a nude or a pastel on your lips. You’ll look really tacky otherwise. This claim is backed up wholeheartedly by my mother, who is a former cosmetologist and model.
Wear decent mascara or false eyelashes.
Seriously, you really need to play up your eyes in cosplay makeup. And if you’re wearing a lot of eyeshadow, it’s easy for your eyes to get ‘lost’ in your face. Having long eyelashes counteracts this by making your eyes look bigger. I wear false eyelashes even for male characters.
Wear the right colors.
If your foundation doesn’t exactly match your skin tone, it’s going to show in pictures and look really silly.
Use some kind of sealer/finisher.
Chances are, you’re going to be at the con from early morning to very late at night. Makeup isn’t made to last that long. A finishing spray will keep it looking fresh all day long. I use The Style Art Designing Makeup Fix by Missha. That is a Korean product, so keep in mind that it’s coming from overseas. You can also use a body paint sealer.
Test your exact makeup plans before the con.
Take pictures of yourself from different angles and in different lighting to make sure it actually looks the way you want it to.
Cover your eyebrows.
This is so, so, so important. If your eyebrows do not match your wig, it’s going to ruin your entire look. There are dozens of tutorials online for effective ways of doing this if you’re clueless. I personally find acrylic paint mixed with a little powder to work well.
Hope this is helpful!