At all levels of swimming breathing is an essential element for the efficiency.
Breathing when you crawl is more difficult because you take in air when you're on your side, which can make the movement of your arms less efficient.
Start to turn your head at the end of the movement. Don't turn before this moment. You can breath every 2nd or 3rd arm movement, but you can also choose to breath after 4, 5 or even more arm turns.
The exhale starts when your head turns out of the water and will become stronger on every impulse.
