The term pricking out means the transfer and separation of young plants that are too close together. For a rich foliage, it is best to choose a leaf day (Cancer, Scorpio, Pisces) when the moon is waxing.
The waxing moon is also generally considered favourable, except in Aquarius.
Avoid the waning moon, especially in Aquarius, so that the seedlings don't hang limp in the ground in a short time.