Often the reason for this is one is new and/or not psychically open enough to sense the presence of the Demon.

Persistence and patience pay off in results.

Satan is strong on one having patience.

Consistent meditation, breathing exercises, and if one is able to, Hatha [physical] Yoga will open your mind and soul.

Hatha Yoga – Library of Rickandria

Again, this is probably because you are new.

Look for subtle signs like candles and/or incense flaring up, and sizzling during the ritual. 

Sometimes if you are psychically open enough, the Demon will physically touch you.

Demons often wait to come to us in our dreams.

Objects can be moved, doors can be open or closed [this is very rare, but it can happen], breezes can come out of nowhere; you may feel the Demon's energy or have other personal experiences not listed here.

Just be open and aware. Look for coincidences.

Do the best you can to come as close to the color as you are able to.

The Magickal Properties of Color – Library of Rickandria

Because of Christian control and pressure, many places where black candles and other colors used in Satanic rituals are sold are becoming scarce.

Your desire and what is in your heart and mind are more important than the candle color.

Candles of all kinds of colors can be found on the internet.

SoSHHial Media: The Jewish Hand Behind the Internet – Library of Rickandria

The first time you summon, ideally, should be done at night.

Nighttime is usually quiet and more conducive to psychic workings.

The energies at night are different from those of the daytime.

The right [psychic] side of the brain is by nature more active during the hours of darkness.

Human Brain – Library of Rickandria

Once you establish a relationship with a Demon, you can summon him/her telepathically at any time by concentration alone, unless the Demon feels otherwise.

He/she will let you know.

If the Demon is busy, which is often the case; he/she may acknowledge you at a later time, usually within a day.

No.

After a relationship is established, just concentrating on and contacting him/her telepathically, with or without his/her sigil should be enough for him/her to show up anywhere or at any time, provided you are extremely respectful and never demanding.

Sometimes a Demon won't show if he/she has a reason but will appear later. 

*When summoning an unfamiliar Demon, you should always perform a ritual.

Demons have much greater amounts of bioelectricity; their souls are much more powerful than that of a human being.

Often close contact results in an excess of bioelectricity that remains with us after the contact. 

Because our physical systems are not used to this, we may experience a heightened energy level and, in some cases, physical discomfort for a short time after the Demon leaves.

When we build up our own bioelectricity, we are able to handle more intense and intimate contact with Demons and not feel anything unsettling.

My own experience has been my skin feeling very sensitized, also like it had been mildly sunburned.