For my own, I used a brush and only glazed the front, leaving the sides and back bare clay. There were a couple of reasons for this. First, I had chosen a clay body that would go well color-wise with the glaze I intended to use. I was happy for the clay to be seen. Second, I glaze fired my frame flat on its back. I didn't want any kiln accidents if the piece should fall over during expansion and contraction in the firing, nor did I want to take a chance on glaze welding it to the kiln shelf.
Once the raw glaze coat has dried completely, your frame is now ready for its glaze firing. When loading the kiln, be certain to give your frame enough space and to position it so no other glazes might drip on it if they should run.