For the drill bit photos I created the large and shallow depth of field by changing the F-stop and putting the camera closer to the drill. The F-stop that I used was 13 and 3.2 for the shallow depth. The picture that is the better of the two is the one with the shallow depth of field. It is an interesting photo because the drill bit is in focus while the background is out of focus. I'd want to use the shallow depth of field to create an object to have a larger feel. You'd use a large depth of field when you want everything in focus.
For the picture of the leaf I just used the leaf as the focal point and used the other leaves as a filler for the negative space. There is a lot of space in this shot and the photo has a shallow depth of field.