Assess your student's skills. They have learned a little bit about reading throughout lives which you could teach them to apply to expanding their reading ability. Alternatively, they could have developmental disabilities that have kept them from being literate. You need to consider all your student's strengths and weaknesses before they can learn to read.
Start slowly. Adults cannot absorb information as quickly without question like children. Adults may become frustrated if you push them too quickly. You can increase the amount of material if your student is learning fast, but make sure not to overwhelm them.
Develop and adjust your lesson plan to fit the capabilities of your student. Most new readers start with phonics, the interpretation of syllables to create flowing sounds or words, and then move on to reading and understanding entire words at a time.
Keep things relevant. While children may be more than happy with stories about ponies or magical castles, adults may prefer to read about current events or more substantial topics. Consider asking your students what they would like to read about as they are learning.