Short vowels are more common in English than long vowels. However, short vowels are often more challenging for English learners because they are unfamiliar with these sounds. If a student speaks a European language such as Spanish or French, I recommend beginning by teaching short vowels before long vowels because of the first language interference. Introducing one short vowel per week works well for older English learners. For younger students, a longer period may be more appropriate.
When teaching any new sound using visuals is extremely helpful. English learners often connect the sound with the object shown and this aids the learning process. Pictures combined with essential English words relevant to the students' lives, is a highly effective method of teaching all sounds. Vowels are more challenging because very few essential English words begin with vowels.
Singing as another mode of teaching vowel sounds. The lyrics below are sung to the tune of 'Frere Jacques / Brother John'. This song is common in many countries.
A has three sounds; A has two sounds. /a/, /A/, /ah/. /a/, /A/, /ah/.
/a/ - apple, /A/ - April, /ah/ - all. /A/, /ah/, /a/, /A/, /ah/.
E has two sounds; E has two sounds. /e/ and /E/. /e/ and /E/.
/e/ - exercise. /E/ - eleven. /e/ and /E/. /e/ and /E/.
I has two sounds; I has two sounds. /i/ and /I/. /i/ and /I/.
/i/ - inch. /I/ - ice, /i/ and /I/. /i/ and /I/.
O has two sounds; O has two sounds. /o/ and /O/. /o/ and /O/.
/o/ - on/off. /O/ - open. /o/ and /O/. /o/ and /O/.
U has two sounds; U has two sounds. /u/ and /U/. /u/ and /U/.
/u/ - up. /U/ - uniform. /u/ and /U/. /u/ and /U/.
As soon as students grasp short vowels, begin teaching words with closed syllables which contain a short vowels.