A couple of  weeks ago I talked about how to narrow down your shots and how hard it can be sometimes to pick out the best out of a series.  I like to do what I call the "Hang It On the Wall Test."  This test is exactly what it sounds like, and is a phrase I often use on the forum I belong to.  You look at your picture, and you ask yourself, "Would I hang this on my wall?" 

The thing with photography is that it can be very subjective.  There are no hard and fast rules for what makes a good photograph.  There are certain things that we may strive for, such as leading lines, rule of thirds placement, well exposed, and proper white balance, but in the end it falls down to the particular viewer's preference.  When I was part of the Science Museum Camera Club in Buffalo we had judges that would say that something was off, let's say depth-of-field.  Depth of field can be very subjective.  Typically portraits are done with a shallow depth of field which blurs out the background and makes the subject pop.  This may not always be the case.  Just because I prefer a well blurred background, but sometimes this can be difficult, and what I consider to be well blurred and what you consider to be well blurred, may be two different things.

The difference in this case?  Whose wall is the photograph going up on?  I may show two different photographs.  Same subject, same background, and for the sake of argument we'll even say same pose.  The only difference we'll say is f-stop.  The first photo will be done with a f/2.8, the second with an f/8.  All else being equal, we'll get two very different photos.*

*When I say "All else being equal," I am assuming that you remember the photographer's triangle of ISO, Aperture, and Speed.  When you change one, you have to adjust one or both of the other two in order to get the same properly exposed image.  To go from f/2.8 to f.8 in this example we have reduced the amount of light in our photo by 1/16th which means that we would need to reduce our shutter speed by the same amount (1/500th - 1/60th), raise the ISO significantly (ISO 200-1600), or some combination in the middle.  Personally, if I can I would reduce the shutter speed only, as I try to use the lowest ISO possible.

In the example above we will only concentrate on the depth of field component which is the aperture setting.  At f/2.8 focus will have to be dead on where you need it to be.  Chances are the eyes and nose will be in sharp focus, and the rest will fall off while the background is completely out of focus.  At f/8 not only will your subject be in focus, but so will your background most likely.

If you're outside then the background may be distracting if it's in focus, if your subject is in front of a backdrop in a studio though, then this may not be considered distracting. 

In the end, all that matters is if you want it on your wall or not.  I hope you found this informative.