Not since the days of Picasso has self-portraiture been so prevalent. Smartphones' high-quality built-in cameras and easy access to picture-enhancing apps are making 'selfies' a ubiquitous form of self-expression among social-media users.

Tina Craig takes and posts a lot of smartphone self-portraits. Ms. Craig, of Dallas, is the 'Bag Snob,' a well-known accessories blogger who has leveraged her large social-media presence (nearly 60,000 followers on Twitter) into a career as an accessories and clothing designer. Ms. Craig has taken hundreds of practice photos of herself from different angles and has pored over magazines to study the poses.

For most people, the most useful self-portrait is the headshot, which can be used as a profile picture for social-media sites like Facebook, FB -2.70% LinkedIn or Twitter. When Ms. Craig takes a close-up, she points the lens directly at her face, rather than using a mirror. (Many devices, including newer versions of the iPhone, have lenses on both sides of the phone so you can take your own picture while looking at the image on the phone's screen.)

For the headshot, Ms. Craig says lighting is important: She stands in front of a window to capture the natural light when possible or seeks a soft but potentartificial source. She angles the camera to capture her face slightly from the left, which she believes is her good side, and lets her face and hair fill the screen. Smile at the camera, she says, even if you feel silly. 'As it is, you're taking a photo of yourself, and that's kind of funny,' she adds.

Frequently, Ms. Craig takes a full-length photo of herself to show how she has put together an outfit. Then she posts it on Instagram, Twitter or Sina Weibo, a social network in China. 'This is a way to show my personal style, and then readers get to know me,' she says.

She usually takes such shots in front of a full-length mirror. Hold the phone with one hand