It is the most frequent of all English vowels because historically it has replaced many unstressed vowels. It has a restricted distribution: it only appears in unaccented syllables.
a. Description: it is very short and weak. The middle of the tongue lies in a relax position and the lips are neutral (neither spread nor rounded).
b. Spelling: this sound only appears in unaccented syllables and it may be spelt with any single vowel or combined with consonants:
-"a": about, woman, chocolate
-"e": sister, the
-"o": synonym, photograph
-"u": suggest, Saturday
Vowels are distinguished by distribution: /ə/ can only appear in unaccented positions and /I, ʊ/ in both accented and unaccented, the rest of the vowels always requiring some kind of stress.
1. Watch this video about how to pronounce schwa and practice several times with the examples given in this webpage:
2. Schwa prediction
3. Pronunciation practice:
3a. Open this chart, click on vowels-monophthongs, then click on central: listen and practice the schwa.
3b.Watch this video and practice.
3c. Listen, read and practice in this webpage.
4. Visit this ESL pronunciation web page and do the exercises provided to practice the schwa.