Despite your best attempts to reduce backscatter during the shot, there will be many times when you will want to remove or hide distracting elements.  Photoshop has number of tools to do, all of which have specific applications, including the spot-healing tool, healing brush, clone/rubber stamp tool, and the lasso tool in conjunction with a dust & scratches or median filter.

Large defects should be removed individually as shown below since filters will likely turn them into light-colored blotches rather than make them disappear altogether.  With experience you will learn which tools to use given the nature of the background or subject.  Best results will be realized using a combination of techniques.  

The blue & green examples are typical of images taken in less than perfect conditions.  Empty backgrounds are easier to fix than those with lots of subject detail but much effort may be required to hide your corrections.  Play with brush size, opacity, density, hardness, radius, and threshold until you discover what works best in each situation.

The Spot Healing Brush provides one-click removal of spots, I try this one first (before)

Spot Healing Brush (after)

Healing Brush copies a similar area for blending over a defect, software looks at both areas to generate a good match (before)

Healing Brush (after)

Clone Stamp also copies a similar area but simply reapplies it over the target area without trying to match what is there (before)

Clone Stamp (after)

Small spots can be erased altogether by drawing around the area using the Lasso Tool.  The selection will be fixed using the Dust & Scratches Filter

Adjust Radius to encompass the largest spots, making sure 'halo-like' artifacts are not created, adjust Threshold (weakness) until area looks natural.

Selected area after first run of Dust & Scratches Filter

Second run of filter on all blue areas.  Notice that the background looks natural with subtle gradations of color rather than a flat blue wall

The Median Filter is a quick fix for areas that look good with plenty of blur with no regard to detail 

Draw selection using Freehand Lasso Tool, Feather 10 pixels, avoid areas where details must be retained

Adjust Radius to blur the largest defects without creating posterization

For smoother results either increase the Radius or Spot Heal larger defects before applying the Median Filter