Preserve the evidence. If there is a defective condition, take photographs.
After an injury accident, it is most important to preserve evidence. If witnesses saw you fall, try to get their names and numbers.
If you fell on a foreign substance (like a spilt drink), you will normally be required to prove that it was there long enough to put the store employees on notice that the condition was dangerous. Witnesses can be vital in that effort. Just because you have fallen in a place of business does not automatically create legal liability.
Document your losses
If you need to miss time from work, it is generally best to get that certified by a doctor. That way, time loss can be proven. Keep all receipts for medical treatment. Many commercial insurance policies will pay a certain amount for medical treatment even without proof of fault (called med-pay). This is similar to PIP on a car insurance policy.
If the injuries are serious, consulting with an experience personal injury attorney is probably wise. Most will handle injury cases on a contingency arrangement, where you will only have a fee if there is a financial recovery from the insurance company.