How many times do you shuffle cards?
Based on several studies, for a good degree of randomness, assuming that a riffle shuffle is used, seven times. Not all shuffling methods are equally effective, and some may require significantly more shuffling repetitions to achieve a good degree of randomness.
You should shuffle cards according to the norm of the game you are playing and what the participants reasonably expect. It is common to shuffle cards for 15 to 60 seconds in many popular card games. Shuffle cards at least a few times to give players a reasonable expectation of randomness.