Purchase an adequate camera. You want a Digital Single Lens Reflex (DSLR) camera that offers the ability to focus manually, change shutter speed and change aperture. Though some magazines prefer film, much professional photography is shot digitally.
Learn photography basics such as composition, framing, lighting, and focusing. You can teach yourself these skills using photography books or by practicing photography until you feel comfortable. Alternatively, take a class in photography basics. Photographers who serve an advertising clientele are called "commercial" photographers, but those who work with magazines are generally termed "assignment" or "location" photographers. Some are photojournalists. In all cases, their work calls for them to "tell the story" that the magazine wants told.
You may wish to give yourself assignments, such as photographing a landscape at dawn, afternoon and dusk. As you practice, you find your photography style and determine your area of concentration. Most magazine photographers focus on one or two types of photography such as nature, fashion, portrait or food photography.
Create a professional portfolio. The portfolio should consist only of your best photographs, in the genre you wish to pursue. Your pictures need to look as if they were torn from a magazine. This means you must adequately plan and set up your photo shoots. For example, if you are shooting fashion, hire an experienced model, makeup artist and hair stylist and provide your model with fashionable clothing. If you wish to pursue portraits, spend an afternoon or day with a model or friend, taking pictures that reveal his personality. You will want a digital portfolio and a print portfolio.
Take advantage of online sites such as Flickr to popularize your work. Contact a local magazine or the editor of a popular blog and offer to take a free set of photographs. Complete the assignment the editor gives you and return the photographs before your deadline. You may wish to spend several months or years shooting for free, until you build your portfolio of tear-sheets, or photographs that appear in magazines. Working with people helps build relationships and contacts in the industry.
Contact magazines and ask if you can send your portfolio over for consideration. Another route to publication is to find a writer whom you respect and find a way to collaborate on a story that you'll pitch together. You may wish to spend time building relationships with people in the magazine industry or other photographers in your genre.