One of the easiest way to control the depth of field is by the aperture. You can open the aperture as wide as possible to achieve the required depth. Another thing you need to take care of is the subject to camera distance. The closer you are to your subject the more the depth of field will decrease.
However, if you pull away from the subject, the subject comes into focus and there is greater focus even without altering the aperture width. One other thing that influences it is the lens focal length of the length you are using. The more the length, the higher the depth of focus.
