If your tradition normally requires you to cast a circle, do so now. If you'd like to play some music, start your cd player. If you'd like to light a candle or two, go ahead, but be sure to place them so that they don't interfere with your line of vision. Sit or stand comfortably at your workspace. Begin by closing your eyes, and attuning your mind to the energy around you. Take some time to gather that energy.
When you are ready to begin scrying, open your eyes. Position yourself so that you can look into the mirror. Stare into the glass, looking for patterns, symbols or pictures -- and don't worry about blinking, it's fine if you do. You may see images moving, or perhaps even words forming. You may have thoughts pop spontaneously into your head, that seem to have nothing at all to do with anything. Perhaps you'll suddenly think about someone you haven't seen in decades. Use your journal, and write everything down. Spend as much time as you like gazing into the mirror -- it may be just a few minutes, or even an hour. Stop when you begin to feel restless, or if you're getting distracted by mundane things.
When you are finished gazing into the mirror, make sure you have recorded everything you saw, thought and felt during your scrying session. Messages often come to us from other realms and yet we frequently don't recognize them for what they are. If a bit of information doesn't make sense, don't worry -- sit on it for a few days and let your unconscious mind process it. Chances are, it will make sense eventually. It's also possible that you could receive a message that's meant for someone else -- if something doesn't seem to apply to you, think about your circle of family friends, and who the message might be meant for.