Answer : There is no single answer to this question since different people have different learning preferences. However, in general, the best way to learn about interior design is to either take some formal classes or lessons from a professional designer, or to dive in and study design principles on your own time. Both of these approaches have their own advantages and disadvantages, so it really depends on what makes the most sense for you personally.
Taking formal classes or lessons from a professional designer is great because you will learn from someone who has years of experience and expertise in the field. This option can be expensive though, so it might not be feasible for everyone. Additionally, it can be difficult to find a quality instructor/program provider in your area.