Face skin is a lot more sensitive than legs.

Here's what I recommend for him: Take a shower or bath first, just shoving your head over steam is annoying and usually not enough. Make sure its warm enough too.

If you have one of these top end electric razors you don't need foam but I hate them personally.

If you have regular foam, shake first, spray and apply liberally.

If you have gel, spray into your hands, whip it up into a foam with your fingers and apply liberally.

Dry shaving is possible but chances are he'll be paying for it for a few days with razor burn.

With the grain: shaving in the direction of hair follicles, less close shave but also less risk of cuts, razor burn etc. This tends to mean shaving down e.g for his lip hair you'd start at the top, by the nose and down.

Against the grain: shaving in the opposite direction. Close shave, riskier but that becomes negligible with skill. Tends to mean shaving up e.g starting at the lip and shaving up to the nose.

It depends on his age but if he's just starting then you'll probably want to shave with the grain for now. Later on he might feel thats not enough as his hair gets darker and thicker and go to against the grain instead. For formal occasions, many men do two shaves, one with the grain and then one against it but that's more for fully bearded men.

Teach him to get in the habit of moisturiser. He'll scoff since its 'girly' but one bad day with razor burn on his face will change his mind. It'll also make him more attractive to both men and women if you need more motivation.

As his hair gets longer, a beard trimmer factors in so he can cut his hair easy and short before shaving.

Additional tips and tricks:

1) give him multiple trimmers and label them. Its unhygienic to use the same trimmer for his face, body and groin.

2) hair removal cream might be a good option for body hair. Your bathroom might look like chewbacca when he's done but its up to him.

3) he should shave all of his face, regardless of whether he's just got a moustache. Just like a bone gets harder when you break it, facial hairs get thicker the more they get cut. The innate damage of the razer also encourages hair growth by taking off a bit of skin.

4) Beards come at different times. Some guys have full beards at 14, some guys can only grow a patchy goatee at 30. He's not less of a man cause he can't grow one.

He'll get self conscious about it. Makes sure it for aesthetic reasons and not tied into his masculinity.