Allah the Almighty commands:
“If you fear that you might not treat the orphans justly, then marry the women that seem good to you: two, or three, or four. If you fear that you will not be able to treat them justly, then marry (only) one, or marry from among those under your guardianship. This will make it more likely that you will avoid injustice.” (The Women 4:3)
Men are permitted to wed upto four women according to our religion. But none of the weddings (nikah) can be performed secretly. All of these weddings must be supervised if it is the first marriage of the bride. The supervisor can be an official or someone from the family of the bride. Weddings which are performed without supervision are void.
Announcing the marriage is also required. According to a narration by Muhammad Hatib al-Jumahi: The Prophet (p.b.u.h.) said, “The distinction between what is lawful and what is unlawful is playing the tambourine at a wedding and announcing it.” (Tirmidhi, Nikah, 6; Ibn Majah, Nikah, 20; Nasai, Nikah, 72)
Aisha narrated that The Messenger of Allah (p.b.u.h.) said, “Announce the weddings, conduct them in crowded places such as mosques, and play the tambourines to announce them”. (Tirmidhi, Nikah, 6)
The most important rule of polygamy is to treat the wives fairly. More precisely, providing the same opportunities for every one of them. Because Allah commands:
“(…) If you fear that you will not be able to treat them justly, then marry (only) one, or marry from among those under your guardianship. This will make it more likely that you will avoid injustice.” (The Women 4:3)
If the husband has a hard time doing this, he should at least keep on doing his essential duties if he still wants to keep the other wife. Allah commands:
“You will not be able to treat your wives with absolute justice even if you keenly strive on it. So at least do not be inclined completely on one and leave the other in suspense. If you reconcile and guard yourselves (against evil), surely Allah will forgive and grant.” (The Women 4:129)
The husband does not need to take permission from his first wife for the second marriage. There is no evidence on this. However, if polygamy is not common in the community living in, the wife will have a right to divorce her husband without giving the Mahr back in this situation. So it is advised that the couple should talk about this priorly.
Please see also:
Women’s Right To Divorce: http://www.islamandquran.org/?p=838