My advice for writers would be: Write because you love to write. Don't think that when you get a book published that you are suddenly going to be rich and famous. Don't take the fun out of it. :)
If you are one of the lucky ones that gets rich and famous that's great, but write because you love to write. Then if you get rich and famous it would be a nice bonus :)
The best way to get sales on your book is to get your name out there. I come across this every day. Authors sign a contract and they think they are done now. :) Wrong, The fun has just begun :)
When you get your book published now the work begins. Join as many yahoo groups as you can, send your book off for reviews, and guest blog. The ideas are endless. People can only buy a book if they know it's for sale.
Another question I'm always asked is, "What do I look for in a book?" For me a story must have a good plot, great characters. A book needs to grab my attention in the first couple of pages or I'm going to put it down. It has to make me wonder what is going to happen from the beginning. I don't like slow starting books that get great at the end. I like them to be great all the way through. I want to feel a connection to the characters. I want to fall in love with them and not want to put the book down.