Having taught pronunciation for about over 9 years, I can confidently say that accurate reproduction of both consonants and vowels is crucial for improving fluency and intelligibility. Investing a little more time on practicing vowels could be more effective to improve the speaking and listening skills of the students. The more you teach pronunciation, the more you realize that the English vowels and pitch (intonation) are indeed inherently connected. You cannot teach one without the other. You might be able to teach word and sentence stress (the English rhythm) without going too strict about the vowels. And to some extent, you might be able to teach them in isolation, but when it comes to practicing vowels, you will find it inevitable to teach pitch.
VOWEL TRAIT 1-HEIGHT
How high or low is your tongue inside your mouth when producing a vowel? Is it all the way in the bottom as in the case of /a/ or /ɑ:/? or is it somewhere in the middle as in the case of the schwa sound or /ʌ/? Or is it perhaps all the way up close to the palate (roof of the mouth) where vowels such as /i:/ and /u:/ are made.
VOWEL TRAIT 2-BACKNESS
Is your tongue making a forward or backward movement when producing the vowel? And how far to the back or front is it really moving? Is it all the way back where /ɔ:/ is? Or all the way to the front where /i:/ is? How about we combine height and backness and start asking questions like “is it back-low or front-high?” etc.
VOWEL TRAIT 3-ROUNDNESS
Are your lips rounded or not rounded? And if they are rounded, do they have the square rounded shape such as /ɑ:/ and /ɔ:/ (open rounded) or tight circle rounded shape such as /u:/ or /oʊ/ (close rounded)?
VOWEL TRAIT 4-TENSENESS
Are your muscles tense (making effort) as in the case of /i:/,/u:/,/ɔ:/,/ɑ:/ etc or lax (not making too much effort) as in the case of the schwa sound,/ʌ/,/ɪ/ etc. at the time they’re producing the vowel?
VOWEL TRAIT 5-LENGTH
Is it the vowel short such as schwa sound,/ʌ/,/ɪ/ etc. or long such as /i:/,/u:/,/ɔ:/,/ɑ:/? Please note that there is separate category known as diphthongs (diphthongs are special vowels that contain 1 vowel + consonant /j/ or /w/. Check out the picture below.
Note:Notice how long vowels are usually tense and short vowels are lax but of course there are exceptions but let us just keep it simple for now.
The English Vowels and their Spellings
/i:/ or /i/
bead, need, happy, key, unique, evening, believe, receive, phoenix, quay, people
bit, gym, women, England, busy, build, sieve
bait, say, face, great, they, vein, eight, straight, bouquet, gauge
bed, head, anyone, leisure, friend, said, says, bury
room, through, crew, truth, fruit, shoe, blue, tourist, do, manoeuvre
book, put, could, wolf
four, board, short, war, door, saw (UK), tall (UK), sauce (UK), bought (UK), taught (UK)
boat, wrote, old, know, toe, sew, though, plateau, brooch, yeoman
/ɜ/ (UK) or /ɝ/ (US)
first, service, nurse, pearl, word, journey, myrtle
body, father, honest, saw (US), tall (US), sauce (US), bought (US), taught (US)
/ə/ (UK) and (US)
about, sofa, listen, convince
/ɚ/ only (US)
Letter, further, centre
/aʊ/ or /ʌʊ/
house, how, plough
/aɪ/ or /ʌɪ/
ride, buy, sky, sign, high, tie, height, island, eye, aisle
boy, boil, buoy