We used a float to press the grout into the tiles. You need to move the float across the spaces at a diagonal to make sure the grout lines are filled. You can then go over it to get most of the grout off the tiles.
In three hours, use a big sponge to remove grout on tiles. This step needs to be repeated in an hour or too. Make sure you have a bucket of water with you, so you can keep the sponge clean. I also used an sos pad in a few places to get grout off.