1. Women who are sealed to other men are disqualified because that would be polyandry. (D&C 132:41)
2. The bride to be must be a virgin and
3. you have to ask your current wife or wives for permission. (D&C 132:61)
4. If the wife says no, she's a sinner and the husband is exempt from practicing polygamy. (D&C 132:65)
5. You have to have babies. (D&C 132:63)
The key concept to understand here is that once a woman has sex with a man, she belongs to that man.
"And if he have ten virgins given unto him by this law, he cannot commit adultery, for they belong to him, and they are given unto him; therefore is he justified." (D&C 132:62)
Virginity is not a gift that keeps on giving - it's a one time trade - , but as long as you can pile on the virgins you're good. Thus sayeth the Lord.