I've tried writing for just fun, and that led to lots of beginnings of novels and many unsaleable short stories. I then tried the "if you want to be a professional, you have to act like one" route. Getting up early to write
every day, learning about markets and saleability, joining rasfc, reading How To books and being a member of various crit groups did improve my writing immensely, but it also led to frustration and disappointment as the publishers and agents didn't agree with the positive things that my critiquers were saying.
So, I have finally decided that I'm going to treat writing as a Beneficial Mental Activity to keep my brain active as I head towards old age. *g* This means that it has to be taken seriously and allocated a time slot in my busy schedule (unlike something done purely for fun!), and if a story seems saleable, I will certainly submit it, but that will an added extra. My aim now is to try to make the writing its own reward. I will endeavour to enjoy the process, the struggles to get the prose how I want it and, finally, enjoy the satisfaction of completing a large project that has stretched over a couple of years.
And writing is a lot more fun than doing sudoku or crosswords, often suggested as activities for fending off senility.