Understand Filters ?
Know when to use one, and their benefits ?
C-PL filters can be a must for certain situations, and its about the only filter than cannot be replicated in editing programmes
Want to know more about filters, and understanding photography? Then feel free to look up my latest dates for my photography classes

Below example of the benefit of a C-PL filter to reduce unwanted reflections

Understanding filters with peterhodgesphotography classes in Cornwall, tuition for beginners, 1-2-1 workshops, evening classes in photography.  A DSLR Course to suit all.  Situation in the heart of Cornwall