Before you begin to teach zero beginners who do not know Roman script, it can help to have some idea of the writing system they use. It may be pictographic, like Chinese, or have a different character for each syllable, like Burmese and the Devanagatri script used in Nepal. Or, it may use an alphabet to build words, like Arabic and Hebrew.
Some teachers find that Chinese-speakers respond well to a ‘whole word’ approach to learning that begins with the overall shape of the word preceding listening and speaking (so the reverse of the usual ELT practice). This mimics the way Chinese pictograms are learned.
Teachers working with students who use a syllabary might find it useful to spend some time focussing on one-syllable minimal pairs like bid, bad, bed, and show what happens when the vowel changes, and when a ‘silent’ letter is added which changes the vowel such as bid, bide, bird, or bad, bade, bard.
Users of Arabic script, including speakers of Farsi, Urdu and Afghan languages like Dari, are not only learning a new alphabet, they have to read and write from left to right instead of right to left and get to grips with English vowel sounds which are not only very different in sound, but are also always written. In Arabic script, short vowels are often not written at all (causing a similar but reverse difficulty for learners of Arabic).
“All aspects of writing in English cause major problems for Arabic speakers, and they should not be expected to cope with reading and writing at the same level or pace as European students who are at a similar level of proficiency in oral English.” Swan M and Smith B, Learner English CUP 1987.