Good language skills are always backed up by good breathing. Learn and practice a deep breathing technique. The trick is to take a long, slow, relaxed deep breath, not a sudden sharp one. Focus on using the full diaphragm. A good analogy is that breathing in is like filling a glass of water.
Q: Where do you fill it from?
A: The bottom to the top.
Fill the bottom of the lungs before you fill the top.
Breathing out we reverse the process: empty the glass from the top first. So empty the top of the lungs first and then squeeze out by tightening the tummy muscles and allowing the diaphragm to rise.