Most people feel awkward doing something new. Being in front of the camera is no exception even through they have probably taken hundreds of selfies with their cell phone. There are lots of resources that can be found by a web search, but I did all the hard work for you and found what I consider some of the best links for you.
I feel the number one reason why people are uncomfortable in front of the camera is they don't know what do. While it is the job of the photographer to give direction, I found this video to be a good start in helping people be self aware and be a little more prepared for a photoshoot.
The next question is what do I wear? I found this awesome blog post by photographer Carrie Allen: https://carrieallen.com/what-to-wear-to-a-photoshoot/. It's one of the best guidelines I have found and no reason to recreate the wheel.
Finally, here are some tips I suggest to prepare for a. photoshoot....both physically and mentally.
This link I found is mostly for women but a great beauty checklist resource by photographer Emily London: https://www.emilylondonportraits.com/blog/2012/10/24/photoshoot-prep.
Drink lots of water leading up to your photo shoot and stay hydrated. Hydrated skin is happy skin.
For Men: Touch up facial hair, manicures are suggested a day or two before. If no manicure, make sure nails are trimmed and clean.
Most importantly...relax and have fun!