Almost anyone can become a model, because there is a wide range of people needed for various products. A model is a set piece. Fashion models are tall and skinny because it shows off the clothes. Lingerie models are thin, busty, and have small hips for a similar reason. If someone is shooting for a workwear catalog, they'll want people who look like they belong on a work site, not Calvin Kline models.
There is one requirement of all models: look healthy. Take care of yourself, especially your skin. Remember that you're trying to have a certain look that photographers will want: while you may automatically associate modeling with thinness, being too muscular or too thin can also be a problem within certain model categories.
Like artists, models have a portfolio of their work. If you are new to the business, hire a professional to take some photos, focusing particularly on your face. Sometimes you may be able to find a local shop looking to hire models directly: this may not pay much, but it will give you something to show.
Next, try out at a modeling agency. Major firms have offices across the nation that you can apply at. When you go in, they will look at your portfolio, and take your measurements. They may take you in for a test photo session, where they will ask you to change positions and facial expressions between each shot. If you can do this quickly enough to suit the photographer, you may have a career in modeling.
However, this doesn't immediately result in jobs. Like actors, models have to go in for casting calls. You may have seen a "cattle call" at your local mall:
In less than a minute, the judges determine if you have the right look and attitude for the product they want to promote. There is no advantage for established models, and even the best are turned down repeatedly.
If getting work locally is difficult, consider relocating to Asia. Non-Asians are very popular for ad campaigns, and getting a job as a model can be much easier than in the West.
Posted 1879 day ago