Ancient Buddhist drawings and sculptures often show people with both hands cupped gently at their lap. Or, one hand on the lap and the other extended somewhat outwards and facing upward to the heavens. This is dhyana mudra. I associate it as the traditional Tibetan mudra for meditation.
Dhyana is the branch of yoga that refers to training of the mind, or meditation. Swami Sivananda likened dhyana to a continuous flow of cognition towards an object. In dhyana mudra, there is a flow of energy flow from one side to the other, providing a sense of balance, physically and emotionally.
While gyan mudra http://thenamastecounsel.com/gyan-mudra-mudra-of-knowledge/ may be most commonly associated with the Indian styles of meditation, I personally prefer dhyana mudra. As with my comments on prithvi or surya mudra, http://thenamastecounsel.com/prithvi-or-surya-mudra-earth-or-sun-mudra/ I believe people should pick a hand mudra that “feels right,” unless directed otherwise.
Indu Arora, http://www.yogsadhna.com/ is possibly one of the foremost experts on mudras in the U.S. A yoga therapist and author of a book on mudras, she lived with her guru in her native India from a young age, soaking up as much learnings as possible. She encourages frequent use of mudras. “Ideally, each mudra should be done three times a day, as the effect will stay with the body for six to eight hours,” she says. “So, we can say, morning, afternoon and evening. The Mudras need to be held for a minimum of two minutes.”