I get a lot of “What lens should I buy?” questions from beginner photographers, and to be honest, it’s challenging to answer with one sentence, or even a few. Each arena of photography has a few lenses that are built for the task at hand, and then a handful of compromises.
If you have any ambition to get paid to take pictures, a great place to start is by photographing people. Start simple. Start with headshots. They are a lot easier to shoot than say a family of five with a sassy 2-year-old.
Headshots with a 18-55mm f/5.6 lens wont sell. They look similar to a cell phone picture. What you need is a medium range telephoto lens with a wide aperture. For example:
Canon EF 50mm f/1.8 II Lens
Canon EF 50mm f/1.4 USM Lens
Canon EF 85mm f/1.8 USM Lens
Canon EF 100mm f/2 USM Lens
Nikon 50mm f/1.4G AF-S Lens
Nikon 50mm f/1.8G AF-S Lens
Nikon 85mm f/1.8G AF-S Lens
All of these lenses do a fantastic job of taking an ugly background, and turning it into a milky-smooth canvas. I often call them beauty lenses, because they help transform ordinary scenes into elegant ones. Photographing a bride in a hotel room, I primarily use my Canon EF 85mm f/1.2 to blur un-wanted clutter.
So, if your current lens lineup is needing another addition, you might want to consider a medium-range fast telephoto. It will help separate your subjects from the background, and also separate your photos from others.