Try on before buying

Things people told me about writing that turned out not to be right (for me):

You shouldn't write in front of a window because it's too distracting.
Avoid adverbs.
If you start writing your second book as soon as you finish your first book, you'll be ahead of the game.
You must write every day.
You can't use italics.
Just write fast. Quantity is more important than quality.
Nobody will buy a contemporary YA with a male main character.
Don't use semicolons.
You have to know what your character wants before you start writing.
Set up Google Alerts so you'll see everything that's said about you.
You'll sell more books if you _________________.
When you publish, everyone you've ever known will come out of the woodwork and friend you online.
Happy endings are considered old-fashioned; don't write them.

I'm sure these predictions and pieces of advice are right for someone ... else.
How does your experience differ from received wisdom?