Plan to put in the time needed to teach the non-reading older student to read. This will generally take 200 to 300 hours of teaching.
Break down the 200 to 300 hours into manageable chunks of time, such as two hour sessions several days per week.
Use a mixture of visual, written and auditory instructional materials to teach the older students to read. The combination of hearing a word, seeing it written and associating it with an image will give the student the best chance of retaining it in long-term memory.
Focus on phonics. Phonics is a concept that involves associating sounds with letters. For example, you need to emphasize the sound that the letter "s" makes, the sound the letter "h" makes and the sounds the letters make when you put them together, such as in the work "hush."
Encourage your older students to read outside of the sessions and supply them with materials. Be sure these material fit with the reading level they're at. For example, you might start with children's books. Then, go toward young adult literature or comic books, and finally, move on to newspapers and magazine articles.
Show your older students the proper way to hold a pencil and type on a keyboard. These lessons may be necessary for illiterate adults who may have never done these activities, or at least not properly. Once they get the hang of it, encourage them to write, just as you encourage them to read. Out of class writing assignments can help.