I would like to study geometric invariant theory and moduli theory. It seems that a standard textbook for these fields is "Geometric Invariant Theory" written by D.Mumford, J.Fogarty and F.Kirwan. However, the book is difficult to read. Is there an easier alternative to this? I would like to read a textbook which makes use of scheme theory.

I read "Algbraic Geometry and Arithmetic Curves" written by Qing Liu from chapter 2.1 to chapter 4.2 and "Algebraic Geomtery" written by Hartshorne from chapter 3.1 to chapter3.4. Also, I understand Cartier divisor and Weil Divisor.