Maximizing Depth of Field

The three ways to maximize the depth of field in your image are:

1) Use a lens with a short focal length: wide or normal lens
2) Focus on a distant subject. If you�re trying to get both a nearby tree and a more distant house in focus simultaneously, for instance, focusing on the house, rather than the tree, is more likely to deliver both subjects in focus.
3) Use the smallest aperture (high f/value) you can, such as f/11 or f/16.
Not unpredictably, you can minimize the depth of field in a picture by doing exactly the opposite of these things. :)

If you don't clearly understand about above, please read The Depth of field: 3 factors