I think your idea of having another person in the class at the beginning is excellent. You’re right to think of teaching communicative phrases in English; by doing this you’ll have the student using English in natural situations and the more he uses English in class, the better.
I think it’s safe to say that there are very few real beginners nowadays. Most people have some vocabulary in English. It’s useful to emphasise this at the beginning. Your student will be more confident if you spend some time each lesson focussing on what he knows. Many languages have words that correspond to the English equivalent; for example in French words ending in “tion” are frequently the same in English. If you point this out to your student and do some work on pronunciation, he will very quickly have a large vocabulary base.
Pictures and real objects are very useful during the early lessons. These can be used to teach vocabulary and phrases such as “is this a ______?” What colour is it? These objects can also be used to teach numbers, alphabet and spelling.
At the beginning, try to include a series of short activities; this could be vocabulary work, pronunciation, listening, teacher presenting a new grammatical structure, speaking. Also try to change the focus from teacher to student frequently. To achieve this, incorporate opportunities for him to speak and activities where the focus is on the teacher (e.g. presenting new language). Learning a language is especially tiring at beginner level; changing the focus will allow him to take a backseat. It’s also important to change the pace; for example after speaking practice, you could allow some time for writing or copying from the board.
You say your student wants to improve his conversational skills; so remember to include practice in listening, pronunciation and set phrases such as you have mentioned (e.g. I don’t understand, can you repeat please).