If I want to be picky, I'll quarantine my plants for a few days so I can catch any live snails that might have been around. I'll also carefully inspect every inch of the plant for egg sacks and remove them. Of course, there's a good chance you'll miss something, but at least you start off with less. Some people QT plants longer to be more careful, but you have to be able to keep the plant healthy during that time. I don't want another tank set up for just plants, so I usually just QT for a few days max before moving to the intended tank.