The most important thing you need to know about the fashion industry today is how important branding is.  Branding is the  practice of creating a name, symbol or design that identifies and differentiates a product from other products.  This is done through product development and marketing.  Everything you do from designing your line to customer service to social media has to have a consistency that speaks to your brand and what your brand stands for.  In this day and age people buy brands they like and have an emotional connection to.
The next thing you need to understand is there is no one way to sell your product.  In fact many brands are disrupting the traditional models of distribution.  Before you sold wholesale to a store and they sold your line.  Then companies started their own stores making and selling their own product.  Think The Gap and J. Crew.  Sometime later the internet was invented and website selling became popular overnight.  Then we got smart phones and mobile became the go to.  Enter companies like Stitch Fix and subscription based selling was born.  Of course there are pop up shops, in home shopping, personal shoppers , etc.  So, think outside the box and really think through thee best way to sell your product.
Mediocre doesn’t cut it anymore.  In the 80’s when I first started in this business it was much easier to be successful.  Nowadays it is much harder.  You can no longer get away with being ordinary.  Your product, branding, and marketing must be top notch in order to stand out from the competition.  There are a lot of brands out there so if you want to grow a successful company bring your best to the market.
Don’t just work hard, work smart.  Keeping your expenses and overhead low is going to be key to maintaining profitability.  Nowadays you shouldn’t have a huge staff.  You need to be lean and mean.  So every part of your business has to run efficiently.  Recently I worked with a company where we moved staff around and not only reduced payroll by a third but by putting the right people in the right jobs we increased sales by 10%.
The business is changing all the time. So stay current by studying the industry daily.