i'll usually prune once in veg, after i top. i give the plant about a week or ten days after the topping, then i'll pick off the leaves that are blocking light from the new growth. thats all i do in veg most of the time. i may end up doing it twice if a plant grows especially quickly.
about two weeks before i put a plant into flower, i'll put it into its final pot. a week after that, i'll lollipop it good, and take a few leaves out of the middle, the ones growing on top of each other and butting up against stems, to improve ventilation and penetration.
once its in flower i prune once when the buds are set well, about week 3 or 4, and i may or may not do it again about a month later, depending on how bushy they get again. and i don't take all the big leaves, maybe half, all the ones that are blocking light and airflow. i tried more aggressive pruning for a while and i think this is better