Aother great exercise is to sit in front of a wall, hold up a piece of paper to the wall, form your embouchure, then breathe out through your embouchure, using your breath to hold the paper up against the wall. Try to see how long you can keep the paper on the wall. Stand further back from the wall and try the same exercise again. See how far away you can be from the wall before it becomes impossible to hold the paper up with your breath. Most new flute players take a breath after every four measures.
More experienced players take a breath after more measures.
Sometimes it depends on where it is more convenient in the musical score. For example, it may be better to take a breath in between a measure if there is a rest sign. As you practice each piece of music, focus on where you should take your breath. Experiment with different places to take your breath to find out which way works best with the music. Always breathe in through your nose and out from your mouth.