By and large, there is no connection between writing sales copy and being able to write a best seller. Skills are way different.
I've written a bunch of books, one of which hit the businessweek bestseller list.
Lot's of decent advice in the other answers, but I'd say if you have to ask these things, you aren't ready to give it a go (writing a book, let alone a best seller).
Advice? Learn the business. Write every day. Start a book. Make writing your profession. (It tends to hurt so this isn't for everyone).
Writing a book (and having it published by a publisher is WAY different from copywriting, article writing, etc.