How to practice thirds

How do you learn to play thirds, as in double stops? Nobody really say anything about the "how". My teacher would just point to the scale book and say "practice, memorize, and play on the stage next week". Sure, we all need to practice. It would help to have a little more detailed steps, or strategy.
Here is mine. Do feel free to share yours in comments.
1. Identify the semitone from 1 pair of 3rds to the next. Mark it out on the music.
2. Feel the semitone in your fingers (touching fingertips).
3. Listen to the intonation, adjust if necessary (especially the whole tone movement, where fingertips are not touching).
Repeat the action again until the movement is fluid and accurate.
Double stop scales for ABRSM and Trinity exams, the 3rds at least, are printed in slurred pairs. So I suggest students to practice each pair until the movement is accurate and confident, before moving on to the next.

Repeating the whole process... that is called "practice". It takes time, and for students, this is a new skill requiring repetitions to gain familiarity. My "strategy" works for me. Anyone may find other strategy works, too. Always experiment around to find your best way to learn.