As a music teacher, I like to start with posture (holding or sitting/standing at the instrument), then move to very basic playing technique (pluck, press key, tap, blow, or whatever). Then simple melodic passages.
Once when interviewing a possible teacher for our studios I asked the candidate what should be taught in a 1st lesson with a beginning student. He replied with "First I'd start with some scales."

I assure you we did not contract with this person.

I'm definitely with Brett and Greg but i would like to also add Rhythm. Melody + Rhythm. In my own experience and observation just these 2 alone will effectively communicate a universal message of all understood emotions n moods to anybody musician or non musician from young to old.

randolf

LOL - Poll is tied 50/50 and then Jeff and Randolf come up with these two (what should be to all of us, me included) quite obvious points.

Jeff is dead on that the very first thing is *how* you actually approach the instrument. I really appreciate randolf's comment because somehow the tutelage of rhythm seems to get left behind in our culture, and it's so fundamental. My wife struggles getting her elementary kids to grasp it--but I've also seen scary examples even in college of people who haven't yet figured out rhythm.

Brett is of course right, as well, that all of this is only a means to a higher level of musicianship. I just had a friend ask me about the dynamics of playing in a group, and I pointed out if I'm focused on the lead sheet and changes, I'm not really playing "with" the other musicians. It's only when I'm past the learning stage and take my focus off that piece of paper where the real interaction and fun begins.

The OP's question has more to do with specifically two means to this end--both of which I would maintain are important, nonetheless. Perhaps what we are seeing here is a lot more than that goes into mastering the craft of being a musical artist. I'm also gathering there's a wider variety of learning techniques that the people on this forum have utilized or experienced in the past than say, a strictly conservatory education or, at the other end of the spectrum, learning to play completely by ear.

I wonder if these same "unmusical" guitarists all wear Ralph Lauren Polo shirts?

Talking about teaching and learning music in general, I agree that you first have to get to know the thing itself (the music as a whole thing) and then can grasp what the ingredients are.

But I understand the question as how one would stack the theoretical knowledge upon each other. For that I would say, Intervals are first as they are the theoretical basis of all music, in my opinion. Then the basic concept of major and minor scales (as a series of intervals), then chords (as a compound of intervals, regarding notes in scales), then the more detailed scale theory for harmonization.