It's best to keep them in some water until your ready to place them in your tank (stops them drying out). A good wash in warm water is highly recommended to remove debris and any unwelcome hitchhikers such as snails. Also, alot of plants are planted in an oasis and this needs to be removed before planting, I soke it in a bowl of water and gently take it away from the roots - works a treat.
This may be helpful http/www.youtube.com/watch?v=44cDbR2YvK4