There are a few essential steps that need to be followed to make the marriage valid(( Mulla, D. F., Sir. (n.d.). Principles of Mahomedan Law (20th ed.) p.331.)):
Proposal and Acceptance
There has to be a proposal made by or on behalf of one person and it has to be accepted by the other for a valid marriage.
Consent
Consent is a very important criteria for a marriage and the criteria for consent changes according to the different schools of law.
Witnesses
Witnesses are those people who are present at the marriage and can state that it took place. They are an important requirement for a valid muslim marriage.
Prohibited Relationship
Some relationships within a family and extended family are prohibited, meaning, one cannot marry these people as such relationships are prohibited under custom. There are strict prohibitions in muslim law which have to be followed.