1) The girl can ask for whatever she likes for mahr but ideally it should be agreed between the man and the woman beforehand including when and how it should be given.
2) The woman has the right with consultation with her family and her spouse to be.
3) It should be in accordance with the society and social status of the woman.
4) Amir al-Mu’minin (‘a) has declared:
عن علیّ (ع) قال: «لاتغالوا بمهور النساء فتکون عداوة.»
Do not set substantial Mahr for women and do not compete in its excess for this causes enmity.