I do not expect you to look perfect and you do not have to alter your appearance to look good. The best photographs are conceived when you are yourself.
Here is what you can do to look your best on the day of the photo session:
Give your hands and nails some attention the day before the photo session and treat yourself to a facial.
Watch out for problem areas in your face, such as oily patches and spots, and deal with them well in advance.
For a couple of days before the photo session, limit your al-cohol intake. Drink lots of water and get plenty of sleep. It all shows in your face.
Do not schedule a photo session when you have just come back from a beach holiday your suntan may be too deep (or worse, a sunburn), you may have tan lines on your body, white watchstrap marks and bright marks around your eyes from wearing sunglasses.
If you are planning to pose nude or in lingerie, wear loose fitting or no underwear for at least two hours before the session to prevent marks.
You may wish to read the makeup pages (women) and skin care for men advice in the models section of my website.