When shooting outdoor shots, it is best to have something in the foreground.  At times though, there will be nothing really there to put in the picture.  An easy fix is to look around for a tree branch or some object and then hold it up (or prop it up some way) that it is included in the border of your picture.  A little branch or flower added for a foreground can create a great deal of depth to your photograph.  

Many times I have held a branch with a couple leaves to dangle into the edge or frame a picture of a sunset.

Now with digital photography, I can easily add them later.