Start with round lips and your mouth open, the way you say 'aw'. Then slide your tongue up and forward until you are smiling — /ɔɪ/, as in 'boy' and 'oil'.
Check yourself: Mirror: round lips at the start, smiling lips at the end. If your lips never change, it is not the sound yet.
Watch for: Splitting it into two separate vowels — 'bo-y'. It is one slide, not two syllables.
◆ marks a word that does NOT follow today's pattern — Blumenfeld boxes these on the page. Teach it by heart; do not let the class sound it out and lose faith in the rule.
Say the word, have them repeat it, count the sounds on fingers, THEN write. The count is what stops a child writing the first letter and guessing the rest.