Liz,

If the surface of the tile is smooth without voids the I would use a
grout float and a grout sponge (a sponge with very small cell
openings) and grout following the directions on the box. It is really
not that messy of a job. Just make sure to get all the excess grout
off the surface of the tile with the sponge (rinse often, wipe at a 45
degree angle to the grout line) before it drys. Done properly, any
remaining grout haze can be buff out with a white scotch pad. If the
tile surface has pits or voids the try a grout bag (same as a pastry
bag).