Hi Joel,
I use a small (2.5cc) syringe to put the glaze into the squares as I find it easier to control how much goes on - as long as the syringe isn't old and no longer runs smoothly from the glaze particles wearing it away (a friend is a vet so I have a good supply of free syringes).
I started with a brush and found it hard to control the amount of glaze in each square, with it often over running into adjacent ones.
Tim