Warmth will cause the flakes to stick together. I personally grind my shellac into a fine powder with an inexpensive coffee grinder prior to mixing to speed the process. This will ensure a great finish without blotching.
Dissolves in denatured alcohol easily; however, if you are lazy like me, you'll need to let it sit a day or two, remembering to stir it occasionally. If you are in a hurry, you'll want to crush the flakes into a powder to accelerate their dissolution. It even comes with recipes for different pound cuts.