For getting best results out of something, one must follow the prescribed procedures. If some doctor tells you to take the tablets with lukewarm water, there must be some reason behind it. Water at normal or cold temperature will not be able to react with the medicines as desired. So you will not get the full benefits.
Similarly, here also, before sudarshan kriya, Bhastrika Pranayam is required. Not only Bhastrika Pranayam but also some other pranayams like 3 stage pranayam.
In general, Sudarshan kriya consists of 3 stage pranayam, Bhastrika, 3 times chanting of Om and then inhale-exhale in rhythm with So-Hum.
For getting best results of Sudarshan Kriya, one has to start with some body warm up exercises, Nadi Shodhan for few rounds (generally 9 rounds) and then kriya.