In 2017.3 a number of improvements were made to the Cloth Physics system such as Brush Based Constraint Painting and Self-Collision Properties. We'd like to make sure that you're aware of all the new possibilities. This post also gives you a general overview of how Cloth Physics work.
In the video below, we've set up an example scene to show you how to get basic Cloth Physics working and some of the constraints you may face. You'll see how to get started with adding the Cloth component to a mesh, how to restrict parts of a mesh from collision physics calculations as well as a few ways to fine-tune the settings of the Cloth component to get the desired material behavior you're after.