1. Expand and contract the diaphragm muscle more energetically.
2. Constrict the throat or nasal cavity.
You will note that method 2 does not achieve increased airflow. Not an original observation, just something I need to work on.
Wind instrument players are instructed to keep an open throat. The reason often given is that the throat resonates with the instrument, improving the tone. I doubt this, I suspect instead a constricted throat is less expressive: changes in diaphragm tension result in less change in airflow, resulting an a less expressive performance. An open throat allows articulation with the diaphragm in addition to tonguing.
This is somewhat like opposing muscles locking a limb in position. It works, the limb is immobilized, but it's also less reactive, and it's burning energy to keep the muscles engaged. A martial artist will therefore try to maintain a relaxed, reactive state. However control of this state requires more practice and attention.