If you are looking to transition to a more sustainable wardrobe I would say the first piece is understanding your color palette and body type. Really learn what flatters you. I also recommend starting with what you have. You are not doing the planet any favors by getting rid of things just because they are not sustainable. Try to revise your wardrobe at least once a year. Take a half day and try everything on. Donate what doesn't work and what you are not wearing and keep the rest. No one starts with a blank slate but the important thing is that you can start whenever. Once you discover the options that are available in sustainable fashion there is really no reason to go back.
The fashion industry is the second largest polluting industry, after the petroleum industry and the implications branch out to environmental issues, labor issues and basic lack of transparency with the consumer. However in the past years, much due to worldwide catastrophes surrounding the fashion industry have given way to new model of consumption. Enter Sustainable Fashion.