You will need to establish that you tripped or slipped on a hazard. Of course, some property owners might quickly fix any problem and deny responsibility. It would be very helpful if you managed to take a picture with your smartphone of the hazard soon after the fall. A picture can helpfully establish that a hazard was present.
In other situations, your attorney will need to get creative at finding sufficient evidence. If you fell in a casino, then security footage should have captured the hazard. Other businesses might also have video evidence, which your attorney can obtain. If no video is available, then we can rely on your testimony and any testimony of other eyewitnesses.