Sudarshan Kriya is a powerful technique taught by AOL (Art Of Living organization).
Best practice is to do minimum 12 sets of surya namaskar ( Sun Salutation ) followed by 3 sets of pranayamas : nadi shodhan pranayama (Anulom Vilom), ujjayi pranayama and bhastrika pranayama in vajrasana. before practicing sudarshan kirya.
It is best if you can continue kriya in vajrasana (Thunderbolt pose) but you can continue kriya in normal spring sitting position also.
Ideally, you should leave a gap of at least two hours after eating your meals before attempting the Sudarshan Kriya.
Sudarshan kriya results in many benefits.
Its the one of the most powerful and joyful meditation / breath exercise technique I have learned in my life.