Breathing with an "open throat" means breathing with the muscles of the throat relaxed. This allows for faster air flow, which can be a help in athletic and musical endeavors. Most people breathe with a "closed throat." This is not to say that the throat doesn't allow air flow, but rather that the muscles surrounding your throat are at least partially flexed. As with unlearning any other long-held habit, the best way to learn open throat breathing is to practice regularly.
Sit comfortably in a chair that offers support. Yoga instructor Kerry Collette warns that some people become light-headed when first practicing breathing exercises.
Allow your mouth to open and your jaw to hang open and loose. This is the easiest and most plainly visible action you can take to relax the muscles in your throat.
Inhale deeply by expanding your diaphragm, filling your torso from belly to collarbone. Breathe only as deeply as you can without feeling discomfort. Your natural tendency once you feel discomfort will be to tense the muscles in your shoulders and throat.
Exhale deeply by pushing from your diaphragm, emptying your torso from collarbone to belly. The flow of air in and out will resemble what happens to water when you fill and empty a pitcher.
Keep your throat and jaw relaxed as you repeat this cycle 10 to 20 times per session.