What to Photograph

You will want photographs of everything to do with the accident or injury. If something caused the accident and is still visible, take the picture. If you are returning to the scene later, chances are the cause of the accident will no longer be visible. Take a photo of the location.
In the case of, for instance, a slip-and-fall in a store, the staff probably will have picked up the material and/or cleaned the area by the time you come back with your camera. What you can do is to place a piece of paper where the slippery material was located, then step back and take a couple of shots.
Even on the afternoon of a dog bite, return and take photos of the dog owner's yard and fence, etc. Won't you be pleased that you have those when the next day a couple of signs appear on his fence or yard that say "Beware of Dog." Maybe you will find the next day that there is a block or post to which the dog is chained. Your photograph taken the day of the dog bite showing no such block or post helps prove your claim. Your photograph the next day showing the precautions the dog owner has now taken may add to the value of your claim.
In those cases, the defendant has assisted you in showing that reasonable remedial steps could have been taken. You might return to the grocery store one month later and find that there is now a rubber-backed carpet runner in front of the vegetable display where you fell on moist linoleum. If you have before and after photos, you can demonstrate that the cost of curing the danger was minimal. If they have not put down a safety carpet, then find a store with safety carpets and take photos to show what could be done.