Tile spacers are an ingenious little invention that eliminates the old floor-tiling dilemma of getting the spaces right between the tiles. These little plastic or foam crosses lie in the intersections between your tiles as you're putting them down, giving you a consistent distance between tiles. The one drawback is that the spacers can't stay there when you grout. Each and every one of them has to come out.
Allow an hour or two for the tiles to start setting up (after you have laid them and have set your spacers between tiles at the corners). Consult your tile adhesive packaging for more exact timing to know when the tiles will be relatively stable to walk on.
Working in sections, grab each spacer with the tip of your needlenose pliers and pull it straight up and out from between the tiles.
Drop each spacer into the paper cup after you take it out. Discard the cup when you are finished.
Grout the floor.
Don't tip over the cup full of used spacers, or you'll have to fish them out of the lines of the floor again. Some people prefer to set the spacers ``tombstone style'' in the crevices, meaning they're standing up instead of lying down. This has the advantage of allowing you to simply grab the top tab of the spacer and pull it out when you're done, but it's more time-consuming when you're laying the tiles.