it's now time to rrrelax.
General note: unless otherwise specified, inhaling and exhaling is usually best done through the nose.
Also known as square breathing, it's a simple and popular technique to help calm the nervous system and help induce a state of relaxation. Use 4s all around on inhales, exhales and holds, or play around with 5s or even 6s all around and see what resonates with you the most.
A technique made popular by Dr. Andrew Weil to bring about a state of calm and activate the parasympathetic nervous system.
Also known as belly breathing, diaphragmatic breathing engages the diaphragm more fully than with our normal day to day breathing. This technique is a little bit more active, so it's often recommended that you first try it out while laying on your back, and not to overdo it. It can help reduce the amount of oxygen needed in our daily life and strengthen the diaphragm.
A variation on the 4-7-8 breathing that might feel more appropriate for you.
Alternate Nostril Breathing (Nadi Shodhana Pranayama)
This additional technique comes from yogic traditions. It's not timed, so you can use something that feels comfortable, like the 5-5 breathing technique if you want to follow a specific rhythm. It's another great breathing technique to calm the body and nervous system. Here's a video demonstrating the technique.
The overarching message is to breathe through the nose whenever possible and to breathe slowly.
If your nose is blocked, here's a simple technique by Buteyko Clinic International to help unblock the nose.