For the AW sound, the lips are still pushed forward but not so far forward as they were for OO. Your lips should be slightly rounded and the lip muscles should be engaged. The back of the tongue still comes up but it is much lower than it was for OO.
For the ER sound, relax your lips, allow your jaw to be half-open and feel that the centre of your tongue lifts up a little bit.
A common fault with this sound is that it can be mispronounced in a way that pushes it closer to the AH vowel – so “girl” becomes “garl”. To avoid this, relax your lip...
