Found a lot to think about in thisnpost at A Newbie's Guide To Publishing:http://jakonrath.blogspot.com/2011/11/guest-post-by-stephen-leather.html
There's a lot ove "I've sold" throughout but once you get past the stats there's a bit worth reading.
His number one strategy: have more than one title out. Name recognition. Sales of one book spur on the others.