The first thing you need to do is inspect the area where you fell. Important questions to try and answer include: What caused you to fall? Did anyone see you fall?
Get the phone number and e-mail of anyone in the general area where the incident occurred - both those who saw you fall, and others who were there after the fall - since they may be needed as witnesses on your behalf if the landowner potentially disputes your claim. Even if no one saw you actually fall, an individual could help describe your pain and the conditions of the area immediately after you fell.
If the incident occurred in a store or place of business, immediately speak with the manager or supervisor on duty. Have them document the incident, and get a copy of anything prepared by the business. If anyone suggests this type of incident occurred before, or they were aware of the condition before your fall, make a note and get the name and contact information of the individual who made that statement. This would potentially imply prior knowledge of the dangers associated with the area where you fell.
Even if the condition that caused your fall is permanent, or temporary (i.e. icy street), take photographs of the area as soon as possible so a record is available. Even"permanent conditions" could change if the landowner thinks you might file a claim for an injury.