Use Pollard's readers with him (available through Google Books). Start with the Primer and work through the Third Synthetic Reader.
Can he recognize the letters of the alphabet in isolation? If not, Handwriting Without Tears will teach that.
If so, does he know their basic sounds? If not, then he needs to learn them.
Here's the kicker where most adult dyslexics get stuck: Can he track letters from left to right? He's most likely not. I'd use a text window for him--you cut a window in a bit of cardstock the height of the text and about a word or two wide, and you place the card over everything else so that the other words don't "jump" into your sight when you're trying to focus on one word. You move the window slowly over text as you decode it.
Then he's ready for Pollard's. Pollard's teaches the student to mark up a word before sounding it out at first, until the student recognizes the patterns automatically. It's really amazingly effective. He needs to go slowly and rely strictly on phonics/decoding knowledge and not try to guess at the words. Adult dyslexia can be the most entrenched, but it's doable to overcome for many people!