When one is looking to get married, he/she should at best, try to consider the following qualities in a spouse. Faith, Morals, Knowledge, and Compatibility; Faith obviously being the most important factor to consider.
A Muslim man or woman cannot marry a Mahram. Mahram relationships on the grounds of blood-relationship include that of:
– Mother/Father (includes grandparents)
– Daughter/Son (includes descendants)
– Sister/Brother (includes descendants)
– Paternal aunts/uncles
– Maternal aunts/uncles
One can also not marry those with whom he/she had relationship on the grounds of nursing, which is established on the requirements of some special conditions (which we will not get too much into)
One can also not marry those people who are declared Mahram on the account of affinity, relationships created by marriage. They are the following:
– Mother/Father in law
– Daughter/Son in law
– A man can not marry his wife’s sister
– A woman can not marry her sister’s husband
Marriage with one’s cousin is allowed.