My landmarks are the G line that for the first intro of clefs for beginners, I actually color pencil in green, and the F line, that I mark in purple (since cannot find a fuschia colored pencil.)
Of course, there is always middle C, and I add a few lessons later, "The Sea of C's" and I color them in blue, and sometimes draw a little fishy nearby if the child is young/fun enough.

I also do a lot of intervals- I turn the page upside down and have the student tell me if it is a repeat, a step (2nd), or a skip (third).

I tell them that there are many ways to learn the notes,and I am showing them several so they can find what works best.

Like, at first with playing, it is finger numbers. Then, note values and note names. Counting progresses from "half-note half-note" to 1-2 3-4, and the same with reading notes.

I shy away from the "All Cars Eat Gas" and such, because-
ask an adult-
which mnemonic phrase is for treble clef? Lines or spaces?

By using LANDMARKS (treble clef marks the G line, bass clef marks the F line, middle C, then the Sea of C's, and later, the G's,) plus intervals, and LOTS of reinforcement with sight reading in a lesson so I can see what they are doing, plus practicing, and it all comes together pretty well.

Oh, another fun one-
at the very first ever lesson, going over keyboard topography, I have them play two black keys and say,
"Hey Diddle Diddle D is in the Middle"
(of two black keys.)

When they learn bass C, I also point out a "new" version of "D is in the Middle" because D is on the middle line.

(yes, the Diddle line D is in Piano Adventures. But, the two black note song I learned from my pedagogy professor.) So there. smile

That is when I tell the students that what they learn as a rank beginner changes over time.

Like a child sounding out words as they learn to read, you would not tell a child reading a chapter book to continue singing the "Ah apple, A ape" song anymore. It is in there.
But, you do keep reading, and writing, and speaking.

Same for piano- you keep sight reading, practicing, doing the theory pages, and sharing.

Learning as I teach.