Can anyone think of interesting ways to portray Depth of Field in photography?

For a University project in crime scene forensics i must show my understanding of shallow depth of field and deep depth of field and i'm trying to think of good examples. I must photograph things myself to show this.

Also any tips on how to really maximise depth of field?

I will be using Nikon D3300 - 18-55mm lens

Yes

Criminal forensics?

How about photographing a bloodied knife (use ketchup or something) from various angles and at various f-stops from wide open to closed down, and argue how convincing they are as photographic evidence. (For instance, the wide open shot might not have enough depth of field to show all the "blood" etc).

To maximise DOF, you can of course stop your lens down as far as it will go. The D3100 is a crop sensored camera, meaning that it will show more depth of field than a full frame one. (If you happen to have access to other equipment, like a full frame camera and a fast prime lens, you can demonstrate the difference in DOF between that and your D3100).

Do your own homework. How hard can it be?

One possibility would to have the weapon on the ground. Get in close and fill the frame with the item and use a small aperture like f/22 to get the whole thing in focus. Conversely you could use a smaller aperture, such as f/5.6 to greatly reduce the DOF which places focus on a specific area. Let's say you want to photograph the weapon with the body in the background which shows where the weapon was located relative to the location of the victim. At f/22 the image would show the body much more clearly while f/5.6 would be much more blurrier.

Another option would to have a series of empty bullet casings and you want to photograph them not top-down which would easily show all of the casings, but if you shoot at a low angle. A small aperture would produce a large DOF to get a lot of the casings in focus while f/5.6 would only get one or just few in focus.

Maybe you've got an item (e.g. Weapon) that has been dusted for finger prints and you want to get just a section of the weapon in focus?

Maybe you could have a series of bloody footprints going through a kitchen floor?

Maybe you have an area where the victim was standing, and you also have the spot further away where the shooter was standing.

I would look through a bunch of real forensic images for inspiration.

Depth of field is something you need to understand but also need to understand that you don't use shallow depth of field in crime scene photos. Frank's answers are for creative work, not crime scene work. There will be an occasion where the shot is going to give some shallow depth of field effects no matter what you do, and you must be able to explain what is going on in the photo in court. You would never purposely set up a shallow depth of field shot.

Place playing cards, standing up, number facing the camera. Place these alongside a measuring tape. Do this on a long table like a park bench. Make sure the measuring tape extends the entire length of the table. Place a card every foot. Focus on the center card only. Shoot a series at every f-stop. Carful, don't change focus position, don't change camera position. Do use a tripod for camera stability. If you can, use the self-timer to set off the shutter. This exercise should do the trick. Best of luck!