Using gravity as your friend, begin at the top and work your way down by spraying your tile cleaner of choice at the top and go toward the bottom. Allow the tile cleaner to sit on the tiles for at least 5 minutes to give it time to work. After this, you can begin scrubbing.
Depending on the porousness of your tile and grout, you may want to use a softer brush to clean with. There are also options for DIY/green cleaning materials if you prefer that.