Clean off your lens. This is the single most important thing you can do to get better pictures out of your cell phone. Just wipe off your lens with your (clean) t-shirt or a lens cloth. Your pictures will instantly be sharper.

Set up some lights. Typical cell phone cameras are not very good in low-light situations. To make up for this, set up some work lights on either side of what you're working on. Your pictures will come out sharper, and having multiple lights will eliminate shadows that can hide key details of the part you're working on. If you can't set up lights, try using a head-mounted light. It will help you see what you're doing, and your pictures will turn out better, too.

Avoid using the flash. Most cell phones include a small flash, and it can be tempting to use it instead of setting up lights. Unfortunately, most phones get confused in the dark places found in your car's engine bay, and you end up with pictures that are over-exposed in the center, and dark on the edges. It's worth trying out, though. Some phones can produce great howto photos using the built-in flash. Experiment and be prepared to take another picture if the flash version doesn't turn out like you expected.

Use a wide-angle lens. When taking a picture of a specific part, it's helpful to provide some context about where that part lives in the vehicle. Often, articles will include a closeup of the part in question, which is great, but it turns into a "Where's Waldo" situation when you need to find that part on the vehicle itself. If you're using a cell phone, pick up one of those cheap magnetic wide-angle lenses (or something like the Olloclip if you're using an iPhone). If you're using a point-and-shoot camera, there may be attachments for it that provide a wide angle view.

Hold your camera steady. Use two hands to hold the camera whenever possible. Brace your elbows against something if available, or hold your elbows tight against your sides. Continue to hold the camera steady until you're absolutely sure the picture has been taken. All-too-often, cell phones will play the camera sound too early, and the picture ends up blurry because you think the picture is done and you move the cell phone away.

Review your photos before putting the car back together. There's nothing more frustrating than finishing up a project only to realize later that you forgot a key step of the process, or the only photo you have of a certain part is too blurry to use.

Take multiple photos of the same step. Try different angles, positioning the tools differently. Pictures are cheap. Take as many as you can to avoid surprises later.

Have someone else be the designated photographer. You definitely don't want to grab your camera when you're up to your elbows in grease, so have someone else (with clean hands) take the pictures.