What are three common ways to propose an amendment?

There are actually two ways to propose an amendment stated in the Constitution and one has never been used.

In the first method a bill or project of law requires to pass both houses of the legislature by two-thirds majority in it. If the bill passes it goes on to the states. This is the way taken by all normal amendments. The second method requires a national convention to be called by two-third of the legislatures of the States and that Convention can propose one or more amendments, these amendments are sent back to the states to be approved by three-fourths of the legislatures or conventions. This method has never been taken.