Sheets and Fabric
The simplest type of backdrop can be created by hanging a solid colored bed sheet or piece of linen so that it falls flat (draping it over a shower curtain works well). When placed in front of an open window or when used with tasteful artificial lighting, this backdrop can provide professional-looking results. Explore different colored fabrics to accentuate your subject's eyes, hair and skin tone.
Buildings and Painted Walls
Walk through the downtown district of your city with your eyes peeled for interesting looking walls. A unique paint job or a well-weathered brick wall can serve as a great natural backdrop, especially if you want your portrait to have urban overtones. Use walls that complement your subject without distracting the viewer's attention from them.
Trees and Foliage
Natural settings are perfect for environmental portraits. Positioning your subject in front of a crop of trees or a large blossoming bush adds texture and interest to the resulting picture. Greenery flatters all skin tones as well as hair and eye colors, and when paired with soft warm lighting, the results are sure to captivate.
Blurred Backdrop
Using a large aperture (wide lens opening) gives a portrait a very shallow depth of field, or effective range of focus. The resulting effect is a sharply focused subject against a blurred, barely distinguishable background. This is a good technique to use when you wish to mask distracting background action or are unable to control the backdrop, as in candid portraiture. A lens opening of f/5.6 or wider will provide a significant amount of backdrop blur.