Take your time and practice each step until you are comfortable before moving to the next.
Leave your SCUBA gear in your bag. You only need 3 things at the pool at this point. 1. Mask 2. Snorkel 3. Weight belt with weight.
At no point will you leave the shallow end of the pool.
Take your snorkel off your mask and put on your weight belt. With your mask on the pool deck, your snorkel in your hand and your weight belt on, get into the shallow end of the pool. You should be where when you stand you are no deeper than chest deep, waist deep is even better. Put your snorkel in your mouth and breathe from it. Now, bend over and breathe through your snorkel while you dip your face into the water. If you are comfortable, stay awhile until you feel natural. If you have difficulty, think about drinking through a straw while you practice the excercise. Remember, you can always stand up straight to end the excercise at any time. If you need to, you can slowly build up your time until you feel comfortable.
Next, practice dropping underwater, allowing the snorkel to flood and coming up to blast it clear, leaving your face in the water. Continue until you are comfortable
At this point, you have accomplished three important things.
1. You lowered your anxiety level by working in a no risk (shallow) environment.
2. You became an expert in no mask breathing.
3. You know you can breathe with a flooded mask.
Now, put your snorkel down and pick up your mask. Put it on and drop down to your knees. Break the seal just enough to allow a small amount of water in. Clear the mask. Do not pull out on the bottom, merely push in on the top while looking up. The biggest mistake most people make is not looking up. The second most common mistake people make is not exhaling through their nose. Keep your mouth closed. Repeat this until you are comfortable. Don't forget to stand up and catch your breath between clearings. Now, increase the amount of water you allow into the mask to about ¼ flooded. When you are comfortable with that level, move to ½, then to a fully flooded mask. When you've reached the point you can clear it easily every time, see how many times you can clear it on one breath. After you are at this point, clearing your mask will be easy. You will have reached it in a step by step manner that was easy to accomplish.
Remember, you can always stand up if you feel uncomfortable.
When you use a regulator, it's exactly the same except for the bubbles. You can tilt your head so most of the bubbles miss you nose. Concentration is important. You aren't inhaling when the bubbles hit your nose, so nothing will go very far. Alternate exhaling through your mouth and nose. As soon as you feel uncomfortable with the bubbles, exhale a bit through your nose. This will push any water out. You'll make it.
