Post processing techniques for removing, modifying or replacing the background abound.
One amazing tool for accomplishing this task is Adobe Photoshop.
One such Photoshop technique is selective coloring. If you have a photo with a cluttered or distracting background, it may be a candidate for selective coloring. Selective coloring starts with the creation of a duplicate image layer in Photoshop. The second layer is converted to black and white and turned into a layer mask. The layer mask is carefully painted in black and white to allow or disallow the color layer to show through. The result is a black and white background and a subject in full color. Selectively colored pictures are attention getting! Here is an example ...
What about landscape photography? Landscape photography is all about beautiful backgrounds. The rules are a bit different here because the background is your subject (you don't want it out of focus). You must be even more attentive to what makes its way into your background. Typically, avoiding items such as wires, telephone poles, unattractive buildings, ... will make shot pictures better. If such objects are unavoidable, remove them later with Photoshop!
When all else fails (or you just want a different look), fill your frame with the subject. If there is no background, there will be no background distractions! This technique works well for portraits of people. Also, try this at the zoo. Remove the man-made surroundings from your zoo photos by framing the subject very tight. The Cardinal picture above uses this technique.
To summarize the above tips ... Improving your photography involves deliberately including or excluding the background from or in your photographs. Getting started is easy - simply be aware!