When I'm studying, I usually do minimal preparation -- perhaps light a stick of incense, but mainly I just try to quiet my busy little mind.
When I'm doing a reading for someone, or a serious reading for myself, I like to have my Kuan Yin statue and something to represent each of the four elements. I have some favorite stones that I find helpful in setting a positive, open energy.
Also, when reading for others, I find pleasantly low light (although not too dim!) helps quiet people who might otherwise be prone to nervous chatter. It's also easier on my eyes.
And I like to have some lavender essential oil on hand, since I find it very calming and rejuvenating if the reading turns out to be draining.