I totally agree with what has already been said, and I'd like to add a few thoughts.

Quite a few times I have seen "oldtimers" or younger experienced modelers who sort of "force" their opinions onto the newcomer. "I only use XXXYYZZZ servos, all others are crap." "That engine will never run right, I only fly XXXZZ." When a newcomer has put a lot of effort and pride into building/assembling his airplane, the last thing he needs is to hear that his equipment is inadequate. I made a mistake myself that opened my eyes. I was the instructor in our club a few years ago, and we had beginners' meetings every week where people would bring their airplanes and work on them. One of the boys had an old 3-channel Graupner trainer that had been crashed numerous times, and it had become quite heavy from the repairs. When the plane was ready to fly, we met at the airfield and I took it up for a test flight. After I had landed, he asked me what I thought about the plane, and The Big Idiot (me) replied: "It's heavy and I can't trim it to fly straight." Naturally, he was very disappointed. He had been working on the plane for several weeks just to end up with a heavy, crooked plane. He quit the hobby, and I never saw him at the field again.

Here's my short list of advice:

1. Encourage him and make him feel welcome at the field.
2. Let him make his own mistakes and let him develop his own opinions and preferences.
3. Let him fly the way he wants to, but encourage him to fly controlled and safely. Not everybody wants to fly 3D, but a lot of people find touch-and-go-circuits boring. Everybody is different.
4. Be an arm's length away so that he can get help when he needs it, but still have a feeling that HE is the one doing it.
5. Have fun.