If the injury takes place in a commercial/retail setting, the commercial general liability insurance of the business owner generally applies. If in a residential setting, a claim should generally be made against the homeowners insurance policy. No matter the setting, as soon as possible, photos should be taken at the scene of the slip’n fall, and the identity of eye-witnesses recorded in order to obtain future witness statements.
Of course, depending on the seriousness of the injury and the urgency of care, this is not always possible. But when it is possible, it is always very helpful in proving your case.