In retrospect, I think the two biggest - if they are separate - mistakes I made are:-
Not jumping on trends and trying to be known as my own writer not a clone of somebody.
I am sure that if I'd tried to copy E.L. James, I could have made a lot more money - http://www.dailymail.co.uk/news/article-3227040/Fifty-Shades-Grey-author-E-L-James-splashes-1million-holiday-home-David-Cameron-s-Cornwall-getaway-village.html.
The two can be seen as separate entities but in my view they are two parts of the same entity.
Back in the day, when I asked by younger writer what is my advice on writing; I always said Be yourself not a clone. These days, I would say copy whose style you want.