Constitutional amendment is but one way that the Constitution has been developed, although it is certainly the most direct. Court opinion, particularly those of the Supreme Court has determined the interpretation of the Constitution. There is no provision in the Constitution for Judicial Review, although it has been considered part and parcel of the constitution since Marbury vs. Madison. Thirdly, the Constitution has been developed by Presidential acts. Notably, when Andrew Jackson refused to stop the removal of Indians from the South he strengthened the power of the Presidency under the Constitution. Similarly, under the constitution, the Vice President has only one official function: to preside over the Senate. Still, a number of recent presidents have vested broad authority in the Vice President. Fourthly, custom and practice have been a method by which the Constitution has been developed. There is no provision in the constitution for a presidential cabinet; but there have been such cabinets since the Washington Administration.
I would say that some specific ways in which the Constitution has been developed is that more people have been brought into the political process. Starting with the Civil War Amendments (13th, 14th, and 15th) where African- Americans saw slavery permanently abolished, rights of citizenship conferred upon them, and the right to vote granted, more people have been included in the process. Women gaining suffrage was included in the 19th Amendment. Young people gaining the right to vote was included in the 26th Amendment, with the lowering of the voting age to 18. The inclusion of people of color, women, and young people were all examples of how the Constitution has been developed over time to include more people in the political process. In addition to this, I think that the fundamental goal of "forming a more perfect union" is represented with these particular amendments as it represents how the framers of the Constitution might have made mistakes early on, and how the self- reflective and corrective measures within the goals of the document allow change and development to be a part of its nature.