Nikki you has inspired me a bit : P
One thing important to cosplayers here is make up! Yes boys even you too.
While photographs are all fine and dandy, and the photographer usually has to work hard to get the good shot, Make up always helps in creating a clean face and making things more elegant and less photo shopping in the end.
There are some BIG parts to make up that I encourage even males to look into before a con where they know their looking for good shots.
Foundation is one of the biggies, just a light coating will do but a bit of foundation can make a world of difference.
This is me before I put on make up for a shoot:
not pretty eh? Theres small brown marks on my face, circles under my eyes, my eyebrows are still dark, and I look over all very monotone and flushed out.
well then this is me after makeup
My face is now smoother, thanks to the foundation, and the blush highlights my face and makes me look more alive, and meanwhile the eyeliner has changed the shape of my eyes a bit.
For looking like a girl there are some very important things to remember make up wise:
1. A good coating of foundation helps smooth out the face and make it less shiny which makes a very big difference in photos. Just put a little on your nose and then suddenly your not going to have a ray of light shining of your schnauzer.
2. A little blush goes a long way. Dont put huge circles on pink on your cheeks, but dip the brush in your blush, and draw it along your cheek bone, feel the the bone, it starts close to the middle of your ear then works its way down and across your face, stop before you get to far to your nose or else it will look like to much.
3. A little lip gloss, just a light pink, or lip stick is even better. Highlight your lips, not big red that shines like a stop sign, but add color to your lips, they tend to get washed out if your taking your photos in a badly lit environment (like cons occasionally.)
4. Eyeliner, it just needs a thin line that runs across the top of your lid and the bottom. One of my tricks to avoid smudging is to hold my bottem lid down with my index finger and feel for the little ledge and draw my line there. Your eyeliner is more prone to smudge if you draw it about under your bottom lashes.
5. Mascara, if your being a girl this is a must. It adds to the femininity greatly.
for boys trying to be girls:
you need to make your face look a bit more slender, hence why the blush is a very good idea as is the lip stick to add some color. there are certain tricks you can do with blush to make your face look more or less different.
For boys:
less make up is perfectly fine, as boys didnt need to look like there wearing makeup or erm it turns out a bit weird.
I do however recommend a coating of foundation, when done right its not noticeable but adds a smoother feel to your skin. And occasionally if your cosplaing more of the bishie type, a bit of eyeliner helps, not much, a good brownish instead of black does the trick well.
and lastly for girls cosplaying guys:
you need a good foundation, and get a brownish blush a bit darker than your skin tone.
one of the tricks used is to get a light eyeliner (brown) and smudge it around your eye lid with a bit of monotone ish eyeliner. it adds a more rugged look to eyes.
then one handy trick is to take the blush (the darker one, it shouldnt be a pink more like a brown) and spread it below your cheek bones, not on but bellow. It makes your bones look bigger and more masculine.
if you have brighter lips, may I suggest a bit of a skin tone lipstick? not to much but just a little really helps!
if you want some more help take a look at these places:
Basic male makeup to look more like a guy for girls:
http://www.youtube.com/watch?v=uUsbjkqUVH4&feature=channelFemale makeup:
http://www.youtube.com/watch?v=pceokOMQycY&feature=channelNear flawless skin:
http://www.youtube.com/watch?v=HmkRR9WlFKs&feature=channelBasic makeup prep by China:
http://snowpeachdrop.deviantart.com/journal/22960695/http://snowpeachdrop.deviantart.com/journal/22961024/A photography guide by Behindinfinity, it also covers some make up advice (even some to help out the guys)
http://behindinfinity.deviantart.com/journal/16401555/well thats all I have to say about make up x_x I'm no expert perhaps this may help a bit in considering tricks to get that right look for the con or a photoshoot
hope that was in anyway helpful