Through a mirror as in "scrying." You will see the Demon in the mirror.
Through the smoke of the incense
The Demon appears directly, when one is sensitive enough and in a deep meditative state.
Prepare your area. Your first summoning rituals should be performed at night. The reasons for this are the energies are different at night from those during the day and it is easier to be alone and free from distractions. When one has established relationships with certain Demons, it is no longer necessary to perform a formal summoning ritual. The Demon can appear to us night or day and all we need do is concentrate to contact them telepathy. This is done by visualizing the Demon [if you can] and/or focusing upon him/her and calling his/her name in your mind.