Basic Guidelines before a class one must note the guidelines before a class
v     It important that you practice with an empty stomach 3 hours of no food. One can do damage to your body if you are doing certain pranayama techniques while the food is wanting to digest.
v     Blow your nose, clearing your nostrils as much as possible before beginning
v     Begin practicing pranayama in a room-temperature. Extremely cold or hot air can affect you health. Have a window open to obtain some fresh air       ( more oxygen comes in)
v     Breath through in and out through the nostrils only, unless otherwise specified.
v     The fluidity of your breath is the priority - if your breath begins to be choppy or uneven, stop what you are doing and allow your breath to return to its own, natural rhythm. Be mindful of your thoughts as they also effect your breathing.
v     If you begin to feel faint, dizzy, flushed, or light-headed, stop what you are doing, and allow your breath to return to its own natural rhythm.  This is a result of the increased oxygen levels in the body, which your body may not be accustomed to. Practice an cleansing breath.
v     Movement compliments the breathing so please wear comfortable loose clothes.

Depending if you are joining a class or having a private session the guidelines are important to follow.