I’m a fresh interior design graduate What is the best way for me to gain and build experience in my field?

First you have to find your way through all Interior Design Styles and try to know which one is suitable for your knowledge and then you'll find your self a big fan of one of these styles, try to practice designs which you see and like, be professional in using CAD programs specially3D Max and have a perfect sketching skills, don't stop you'll be there.