As an approved photographer on stock libraries, you can possibly get access to client briefs where you can submit your work direct to the client, meaning they’ll consider you for the project and see your profile. Otherwise there’s usually a marketplace type system for you to upload your images and have them added to collections based on themes, destinations and seasons.
A pretty picture is not enough. It needs to be high quality and it needs to be original. For magazines, you need to consider issues such as leaving space on the image for word placement, positioning your subject off-centre so it doesn’t fall down the page join, and possibly placing the subject on the right-hand side of a landscape shot for maximum impact.