Tenm Laida is, IMHO, the easiest of the three techniques to perform. The way in which I use Tenm Laida is as a method to achieving that altered state of conciousness in which that other realm may be contacted. This state is acheived through the chanting or singing (or as many of us seem to be utilizing more shamanic techniques - drumming) a repetitive phrase or pattern, until the mind reaches a state of inner peace. It must be noted that this seems to be a universal practice, forms of it may be found in most native cultures.
Whilst using this technique the Filidh would often prophecise in the form of spontaneously composed verse, (though I have to be honest and say I`ve very rarely achieved it!).

Describing how Dichetal do Chennaib worked it problematic. In the Senchus Mor it is translated as incantation from the ends (of fingers), or (of bones). Others translate it as inspired incantation or cracking open the nuts of wisdom. It could mean that the `poet` would compose a Ogham `spell` using the fingers to make the Ogham shapes. Alternately a  kind of Hand-Ogham may be been suggested, each Ogham used as a mnemonic to compose inspirational verse. What ever its form, it was the only technique that St.Patrick did not outlaw, because, unlike the others, it `contained no ritual`.

Imbas Forosna, seems to me to be related to the Tabhfheis - `The Bulls Hide Trance`. Both involve the `poet` chewing on the raw meat of certain animals, both involve sensory derivation, (Tabhfheis beneath a bulls hide, Imbas Forosna within a darkened chamber) and both involved prophecy whilst in a trance-like state. In Imbas Forosna the `poet` would remain in the chamber for up to three days, and would then be brought out into the bright light, the sudden illumination causing spontaneous prophecy. Now the one thing I was always taught is never to shock someone out of  meditation, so I can`t recommend this at all. The Filidh were trained for up to twenty years in these techniques, we, as a rule, are not