Hey edgar, I'm stickin' in my two cents' worth.
Use a big glass. Put in a little more syrup than you might use for a chocolate milk.
Add milk--about a third of the way up. Stir.
Add seltzer. It must be absolutely fresh, not a day old. Without fresh seltzer you don't get foam. Without foam you don't got an egg cream. Stir.
Don't fill the glass all the way to the top. You need room for the foam. And it will foam. Trust me.
Slurp, Do not under any circumstances use a straw. Anybody who serves an egg cream with a straw is a novice and doesn't know the world of the egg cream.
If you do it, let me know if you like it.