I recently met a club player who had been playing chess for 23 years, but couldn't improve his ELO more that 1800. When I played with him, I found his tactical skills are good, moderate endgame knowledge (excels in rook endgames) and poor opening knowledge. Afterwards we had a chat and I could uncover several myths in his mind such as knights are superior to bishops, two rooks will never beat a queen etc. If I am tutoring a student like him, how would I go about teaching him. My first impression is to make him unlearn the 'myths' in his mind, teach a few opening lines helping him to understand basic principles like developing pieces quickly, controlling the center etc.
Teach him by showing example positions that you can play out against each other. There is a big difference between being told that two rooks are often stronger than a queen and really experiencing the power of the two rooks. You could maybe play out a position from the Kramnik-Leko match 2004.
You can try and show him the games played by legendary players like Bobby Fischer, Paul Murphy, Emmanuel Lasker, Jose Capablanca, Alexander Alekhine, Garry Kasparov, Anatoly Karpov etc. Moreover, for any chess player , reading the following book is a must. It is the BIBLE of Chess. The book is named MY 60 MEMORABLE GAMES by Bobby Fischer. Watching these games and reading the annotations not only increases the chess knowledge but is also great fun. For such a senior player I think this is a good way to teach him.