I painted a cement porch once. If it's never been painted, just clean it well and paint. If there's old paint, use wire wheel to scrub off loose chips and clean things up so you have level clean canvass. Again, try and pick a day not so humid. Stay off it untill completely dry, add however many coats you need.
Lisa is right but be sure to pick paint for cement so that it sticks and wears longer and better.
here are some ideas:
Sweep and vacuum the floor very well to get everything off of it and then use a roller and get him some gray flat or semi gloss or eggshell paint finish so that’s a slippery when wet and use a roller and just roll the whole thing but try gray battleship gray
Use paint intended for concrete. Make sure it is very clean, first.