People rarely slip on a clean, dry floor. Contamination is involved in almost all slip accidents, that is anything that ends up on a floor, eg rain water, oil, dust etc. If a floor has a smooth surface (eg standard vinyl, ceramic tiles or varnished wood), even a tiny amount of contamination can be a real slip problem.
Contamination can be introduced by the work activity or by cleaning.
Encourage a 'See it, sort it!' mentality to deal with hazards quickly, eg dealing with a spillage, instead of waiting for someone else to deal with it. See Slips and trips - Hazard spotting checklist and Stop spills in kitchens: A good practice guide.