Shaving the head with a straight razor can be very difficult and time consuming, depending on the skin and thickness of the hair.

To get started, the best thing would be a good quality soap and brush, and a double edge safety razor. Once he's got that down and the skin is used to it, it would be good to move on to a shavette (disposable blade straight razor) and then eventually a straight razor.

FWIW, it took me almost a year to be able to do a complete head shave with a straight razor. I still mostly use a safety razor, to save time. Only once every few months do I do a head shave with a straight.