You need to move close to the dog to see the damage. Walk towards it slowly, keeping eye contact and speak in a slow, reassuring tone. If it barks or growls at you, step back. Try to find some food and use it to gain its trust. Don't touch it yet until it shows that it trusts you. Its facial expressions should give you signs if it will allow you to touch it.
Secure the Dog
Pet your dog and give him or her the reassurance that things are going to be OK and that you're doing something about the pain. Tie a leash around its neck. If you don't have one, use a tie, a belt, a rope, anything that you can use to make a make-shift leash. This will let you handle it better. Muzzle it to top it from biting you. Slowly and carefully lift the dog up and take it to a safe area.
If you Can, Know why the Dog Got Into the Situation
It's best to figure out why the dog got hurt to start with. This lets you pinpoint possible areas that also could have been damaged. Even if the dog does not have cuts or bruises, it could have gotten injured from the inside. If the dog has an illness that causes it to become partially paralyzed or unable to move, like degenerative myelopathy or arthritis, its best to check if it can still move of feel its legs. It could have gotten hurt because of sudden loss of control over their lower limbs.
Apply First Aid
Stop blood from open cuts by placing clean cloth over it and securing it to place. Run your hands though the dog's body and check when it reacts to pain. Dogs who are paralyzed or have degenerative myelopathy may not feel the pain since their nerves are not working properly, but be watchful for any reactions.
Take it to the vet
Carefully carry the dog to the car and take it to the veterinarian. If you don't have a way of transportation, you can call the vet or a veterinary ambulance to pick the dog up. Many animal hospitals have emergency rooms where they can run tests like x-rays to check internal damage.