Marketing... Where do I begin

Would anyone be able to offer any advice on how to get your marketing off the ground and be effective?

My goal is to flip 12 to 15 homes a year.
I know that I want to target motivated sellers.
Which market is the most profitable??
For example are acquiring Pre-foreclosures more profitable than finding a motivated FSBO who is divorced?

How and who should I be marketing to in order to ensure that my time and money is being spent effectively??