[I learn English by myself] - SCHWA SOUND

    In this American English pronounciation, pronounce the schwa vowel sound. This vowel is always unstressed. The mouth position is a lot like the UH as in and usually is streesed. But just like that vowel, everything in your lips, jaw, and neck should be relaxed for this sound. The trick is to keep everything. Let’s look at the vowel up close and in own with the slightest jaw drop. But in actual words, you will likely see a bit ‘sofa’. Lips relaxed, cheeks relaxed, tongue forward and relaxed. As I said, this vowel can only be in an diphthong sounds can either be stressed or unstressed. So the schwa will always be really fast and low in pitch. Uh, uh.

The schwa goes with the syllabic consonants L, M, N and R. That means followed by one of these consonants, you absorbed by the next sound. For example, the word ‘father’ just go from the TH sound right into the separate schwa. 

Example:

allow, extra, data, again, visa, about

Source : Rachel's English