Some people are naturally photogenic. No matter what they are doing or what they are wearing, every photo comes out like something in a magazine. I am not one of those people. I'm usually caught while talking with one eye half shut.
As a published author or illustrator, you are now a business. Your photo needs to convey a sense of professionalism as well as showing who you are. Writing thrillers? Maybe a dark and broody shot would work. Goofy humor? Colorful and full of light and laughter may portray you best.
If you can, hire a professional photographer. It is a business expense that you can write off at the end of the year. Or tell a loved one, all you want for your birthday is a 30 minute photo shoot.
Amateur Example: I took this photo with my really nice camera I bought on a Black Friday Deal a couple of years ago. We took like 30 shots and this is the only one I didn't hate.
I paid for a 30 minute session. We met at an old library. She took a bunch of shots, sent me about 15, and I seriously like all of them. With her lighting, superior equipment and artistic eye, she made me look younger and like I'd lost 15 pounds. She gave simple instruction like, "chin out a little more," or, "lean forward slightly," or, "That yellow background is washing you out. Lets move over here."
This looks professional, flattering, and the high resolution means it will maintain its quality even when resized. This is important since you'll be sending this file to interviews and author/illustrator visits.
A few tips: Tiny print on your clothes doesn't always translate well on camera.
Some poses feel awkward but look great on camera.
Stop to relax you face after holding the smile for so long.
Call around to photographers. I don't believe the one I worked with advertised a 30 minute session, but when I explained what I needed she said a full hour session was unnecessary. Although, she started having fun with some shots and we did go a little over our time, but she didn't charge me extra.
Also, HAVE FUN! For that photo session, you are the star.