NG-AY, NG-OO, NG-AH
In your mid range, sing on an NG, and open to an A (the vowel of May) vowel - like Sing-A, Sing-A, Sing-A, on one note starting at F4 or F3 go up to around a D5 or D4, and then switch to Sing-OO, Sing-OO, Sing-OO and go up to around A5 or A4, and then go back to F4 or F3 and work down with Sing-Ah, Sing-Ah, Sing-Ah. This amazing exercise I have created will center and engage the breath and breath control, find the placement and cord closure before opening up to bloom the resonance. Remember as you "buzz" on the NG you are actually singing, just that the "sound" is blocked back from the tongue. Simple exercise that leads to complex results!