Your injury case will probably take a while to be resolved. It can take months, maybe years, to get a fair settlement. You must act quickly to preserve evidence that you may need later.
Proving Negligence
Before the other guy's insurance company will pay you, you will need to prove that the other driver was negligent. Maybe the negligence was obvious, but maybe not.
Preserve how the accident scene looked with a few photos. You wouldn't be the first to be surprised by changes later made in an intersection. For instance, the city might change the signage or tear up concrete and curbing.
Don't depend on law enforcement to take the photos you might need. While well-meaning and typically thorough, they are not required to take photos. They don't always get the photos you might need and they are not required to keep the photos for a long time. Be proactive and take your own.
Proving Pain and Suffering
Even if you are able to prove negligence, you must also prove pain and suffering before receiving compensation.
Take pictures of your physical injuries. Here is where a picture really can be worth a 1,000 words. For instance, it is one thing for medical records to say your head required 24 stitches for closure and quite another to produce a color photo showing your bruised and discolored face all stitched up.
While no one likes having their picture taken under these circumstances, such a photo can be invaluable later when the insurance company is scoffing at you and saying your injuries weren't that bad.
If you are in pain, keep a journal. Later, if you are asked how many headaches you suffered through and what the degree of your pain was, you will have physical evidence. You can use whatever feels comfortable: a tablet with dated pages, a diary, or even boxes on a wall calendar.
You won't remember all that happened months from now when you need it, so write it down now. A wise man once said, "A 29-cent notepad can be more valuable than a million-dollar memory."