Which technique is your favorite ? Or one you would advice people to do?
I love the 4 season breathing technique (found it in Damien Echols book)
Close your eyes.
Think of springtime, see/feel/hear/touch everything link to that time of the year.
Inhale the energy, counting to 4.
Feel the energy of Spring inside you. Exhale.
Do this for the 3 other seasons
My fave is the lemniscate technique by Assad Splieth 
I imagine a lemniscate in front of me and I follow the shape of the lemniscate with my breath. Breathing in through one nostril (not physically, I simply imagine that my breath passes one nostril at a time!) along the first half of the shape, releasing my breath through the other nostril for the length of the second half of this lemniscate. Breathing into a circle instead of in and out gets me faster into the blank head space 
My favourite is the secret smile technique from Path Notes of An American Ninja Master.
Tighten your toes, hold for a moment, then relax them. Do this three times.
Pay attention to the relaxed sensation caused by the release of the muscles, and fill your body with it, bringing it up your legs, thighs, your chest, flowing down your arms, wrapping around your back, moving up your spine, and over your head with your breath. Catch the feeling with your tongue, mix it with your saliva, and swallow it down to the bottom of your belly, where you swirl it around.
Next, think of a time when you did something you not only felt proud of, but that other people recognized your achievement. Erase the people, and events, and focus on the feeling. Take that feeling down to your toes and breathe it through your body like you did with the feeling of relaxation. Bring it over your head, mix with saliva, swallow and let it mix with the feeling of relaxation. Breathe both feelings through your body for three or more cycles of breath.
Remember a time when you were laughing so hard, you totally lost it. Take out the joke or event and focus on the feeling of wild laughter. Breathe the feeling through your body, swallow it, and allow it to mix with the other two feelings, and then breathe all three through your body.
Remember a time when you were in love, and feeling loving. Breathe that feeling through your body, swallow it, mix it with the others, and then breathe all four through your body.
Remember the best orgasm you have ever had and breathe that through your body. For men, focus on the feeling just before ejaculation as the male orgasm tends to be too short for this exercise. Mix the feeling of orgasm in the belly with the other feelings and then cycle all five through your body with the breath for three or more cycles.