First, take care of yourself — but if you are able, a few steps protect your claim. Report the fall to the store, manager, or property owner and ask for a written incident report. Then photograph exactly what caused the fall — the spill, the broken step, the ice — because it can be cleaned up or fixed within minutes and is the single most important piece of evidence.
Get the names and numbers of any witnesses and the staff you spoke with, and note the date, time, and location. Look for surveillance cameras and note where they are, so the footage can be preserved before it is overwritten.
Get medical care even if you feel able to walk away, because some serious injuries appear later and a gap in treatment is used against you. Finally, be careful about giving a recorded statement to the property's insurer before you have advice — an early statement is often used to blame the injured person.