Setup:

The ritual is best done at dusk, the liminal time between day and approaching night.

You'll need at least three people to help with the ritual, four if you can't sing yourself, for An Cronan Bais . These people should be able to sing the traditional Scottish Gaelic song used in the rite.

The ritual can include a potluck feast in honor of the dead if you wish, or food offerings can be prepared ahead of time to be offered to the one who has died. Favorite foods of the one who has died are very appropriate.

Prepare an altar space with a table or flat area for candles, offerings, and images of deity or other images. Ideally this should be in the west or south-west, which are the directions of the ancestors and the land of the dead. You will need photos and mementos of the person who has died. If you have an image of Manannan of some sort, this is very appropriate. The altar should have wall space behind it for hanging pictures, or shelves set up for putting up pictures, written notes, or holding mementos of the dead.

The altar should be pre-set with a basket or bowl of apples or other fruit and/or nuts (hazels are best, but others are fine) as a preliminary offering in the ritual. Boughs of yew can serve as decorations as well, for their connections with age and immortality, though any evergreen will do.

Ask people to bring photos or mementos of some sort of the one who has passed on. 

You'll need candles (tealights in their cups are great), incense of some sort if you like, and plates and cups for offerings of food and drink.

You'll need a small container of honey, and one of salt.

Proceeding with the ritual:

Welcome the people into the space in any way you wish. It's traditional in the Highlands of Scotland to welcome people with a sip from a quaich ( cuaich or cup, but in this case a shallow one with two handles, usually used to ritually serve a sip of scotch to everyone). The quiach doesn't have to contain alcohol. Any liquid will do. Welcome with appropriate words for the memorial.

The ritual is for feasting and welcoming the spirits of the one who has passed. It is a profound occasion, but not one that must be solemn. The feast is not a dumb feast. It will not be held in silence, but if people wish to keep silence, they may.

When the guests have been welcomed, have them put their photos and mementos of the one who has passed on the altar. 

Smudge the area and people with juniper smoke or have some juniper oil in a diffuser. Juniper was traditionally used in Scotland to purify the house at the new year. This is just a smaller-scale treatment of the idea.

When this has been done, pass around the small container of honey. Each person should take a bit of honey and put it on their tongue (or mimic the action if they have trouble with sugar).

The honey represents the sweetness of life. You can speak of this as the honey is passed from hand to hand. You can be as short or long about it as you like, but short and sweet is best.

Pass around the container of salt. Each person should likewise take a bit of salt and put it on their tongue. The salt represents the bitterness of death and parting. Again, you can speak of this as you've spoken of the honey.

When this is done and all have partaken, at least in gesture, pray to Manannan mac Lír. He acts as the psychopomp or guide of souls to the land of the dead.

Prayer to Manannan in Irish/English:

Manannan, a Thírna nan cheó
éist le ár ghuí agus osclaím nan n-geatai bíseanna
Manannan, a Loingseoir Mhór
Stiúradh sinn,
Más é do thoil é, spré do clóca-cheó
agus beir [name] a Tír na n-Óg. 

Manannan, Lord of Mist,
Hear our prayer and open the Spiraled Gate.
Manannan, Great Navigator,
Steer us,
If it please you, spread your mist-cloak
and bear away [name] to Tir na n-Óg.

Light a candle for Manannan on the altar.

The song An Cronan Bais is sung by the Anamchara or soul friend of the dying. Three chanters join in the song at the indicated places. Sheet music is available from the link on the sidebar.

Anamchara:

Thu dol dhachaidh an nochd do'n t-sior thigh Geamhraidh
Do'n t-sior thigh Foghair is Earrach is Samhraidh
Thu dol dhachaidh an noch an seirm nan Filidh
'S geal deithe 'gad fheithemh air bruaich Tír na n-Óg
Manannan Maraiche 'na do shuain
Brighid ban-leighis 'na do shuain
Gach eile deithe 'na do shuain

You're going home tonight to the house of Winter
To the house of Autumn and Spring and Summer
You're going home tonight on the music of poets
Bright Gods await you on Tír na n-Óg's shores
Manannan, Sea-guide with you in sleep
Brighid the Healer with you in sleep
All other deities with you in sleep

Chanters:

Caidil gu ciuin Caidil gu ciuin

Sleep gently, Sleep gently

Anamchara:

Caidil a luaidh an uchd do Mhathar
Caidil a luaidh 's i fein 'gad thaladh
Cadal a' Fhionn an uchd na h-oighe
Caidil e caidil e 's dhiot gach bròn

Sleep my dearest on the breast of your Mother
Sleep my dearest though you love this place
Sleep of Fionn on the breast of the night
Sleep, o sleep without any sorrow

Chanters:

Caidil e caidil e 's dhiot gach bròn
Caidil e caidil e 's dhiot gach bròn

Sleep, o sleep without any sorrow
Sleep, o sleep without any sorrow

Anamchara:

Cadal òg Oengus
Cadal beò Oengus
Cadal gloir Oengus

Youth-sleep of Oengus
Life-sleep of Oengus
Glory-sleep of Oengus

Chanters:

Caidil e caidil e 's dhiot gach bròn
Caidil e caidil e 's dhiot gach bròn

Sleep, o sleep without any sorrow
Sleep, o sleep without any sorrow

Anamchara:

Cadal gaoil Oengus
Cadal muirn Oengus
Cadal ciuin Oengus

Love-sleep of Oengus
Joy-sleep of Oengus
Gentle-sleep of Oengus

Chanters:

Caidil e caidil e 's dhiot gach bròn
Caidil e caidil e 's dhiot gach bròn

Sleep, o sleep without any sorrow
Sleep, o sleep without any sorrow

Anamchara:

Cadal nan seachd buadh ort
Cadal nan seachd luan ort
Cadal nan seachd suan ort

Sleep of seven victories on you
Sleep of seven moons upon you
Sleep of seven deep-sleeps on you

Chanters:

Caidil e caidil e 's dhiot gach bròn
Caidil e caidil e 's dhiot gach bròn

Sleep, o sleep without any sorrow
Sleep, o sleep without any sorrow

Anamchara:

Bruadar Brighid is Daghda 'na taobh
Bruadar Donn an I nan naomh
Bruadar leinibh nach cinn gu h-aois
Bruadar cadail gach aon do m' ghaol

Dream of Brighid with Daghda beside her
Dream of Donn in the Holy Isle
Dream of the Child who never ages
All these dream-sleeps on you my love

Chanters:

Bruadar cadail gach aon do m' ghaol
Bruadar cadail gach aon do m' ghaol

All these dream-sleeps on you my love
All these dream-sleeps on you my love

Anamchara:

Tha duibhr' a' bhàis-chadail a luadh 'na do shùil
Ach caidil gu ciuin
Caidil gu ciuin
Caidil gu ciuin
An ainm na deithe slan le do phiantan
Manannan air tighinn 's tha sith 'na do ghnuis
O Manannan air tighinn 's tha sith 'na do ghnuis

The darkness of death-sleep, my love, is in your eyes
But sleep gently
Sleep gently
Sleep gently
In the name of the Gods, a cure for your pain
Manannan's come bringing peace to your face
O Manannan's come bringing peace to your face

Chanters:

Caidil gu ciuin Caidil gu ciuin
Caidil gu ciuin Caidil gu ciuin

Sleep gently, Sleep gently
Sleep gently, Sleep gently

Introduction to the altar:

At this point the anam chara and the chanters or other altar attendants will introduce each individual to the altar. Whether or not the anam chara will need assistance will depend on the number of people attending and the way the space is arranged.

Each person in attendance is taken by the hand and introduced to the altar. They are told:

This is the altar for [name], your beloved dead.

Place their hands on the basket/bowl of fruit.

These are offerings for [name]. Call upon [him/her] this night, and sit vigil with [him/her]. Light a candle for [him/her], and call [him/her] home.

At this point, the person's hand is released and they light a candle on the altar. If they're so inclined, they may call upon the one who has died aloud and offer prayers, or they may wish to contemplate silently. When they are finished, they may go to their seat at the table.

When the invoker and/or altar attendants release the hand of each person, they go back and get the next person, until each person has been introduced to the altar. It's good to have a large altar space if you'll have a crowd, so that many people can be at the altar at once.

Once everyone is seated, the feast is brought out and set upon the serving tables. Before anyone is served, plates are made up with a sample of each of the kinds of food in the meal. The same is done with the various drinks brought for the feast. If there is a lot of food, you may wish to offer different plates for meat, for veggies, for breads, for desserts, etc. If there is no feast for this rite, the previously prepared offerings may be brought to the altar now. The plates are carried up to the altars and offered to the deceased. [He/she] is asked to accept the offerings.

Once this is done, if there is food, everyone else may begin serving and eating. People should be encouraged to share stories of the recently departed, to honor their memories. Songs may be sung, photos passed around, and other ways of sharing and honoring the life of the deceased encouraged.

Thanks to Manannan and the spirits:

These thanks can be done extemporaneously. It's not a "dismissal," it is literally a thanking of Manannan for opening the mists and carrying the deceased to the Otheworld. No formal invocation of Manannan was done, only a prayer was offered.

At this time, candles should be extinguished if the space will be emptied, or left to burn if someone will be there to attend the space until the tealights burn out. People can take home the candles they've lit if they wish. 

Once this is done, the food and drink offerings can be taken outside to an appropriate place and left for the spirits. In the Scottish tradition, once the food has been taken by spirits, the toradh or life essence of it is gone, and it becomes unfit for human consumption. The word literally means "fruit, produce, yield" but is also used in this poetic sense.