I would love to hear some string teachers address their sequences for vibrato. My own (still evolving) is...

1) Polishing the string
2) Polishing the string while the thumb stays in place
3) Slowly applying pressure until the left hand finger is rolling instead of sliding
4) Practicing at different speeds with a metronome.

Step 2 is a big one for students to make and takes a lot of individual instruction to keep the wrist from flexing. Is there an extra step that would make my students more successful?