And one more thing that really helped me go from crow to nightingale:

1. If you can, try yawning on purpose.

2. While you're doing it, pay attention to the way your throat (right at the back of your tongue) opens up when you do.

3. Now try doing that on purpose.

4. Now try doing that on purpose, while singing.

As soon as you can sing with that opening, you'll hear a major improvement in the sound that comes out. I even knew a woman who deliberately yawned through every note of "Summertime" and it was amazing!