The business value of EA only becomes truly clear (beyond simply reducing costs in the IT infrastructure) when you begin to think of SOA as a strategy for implementing EA. Then the architecture effort has a built-in business goal: create an architecture designed to deliver services to the business in terms it can understand. Simply put, it's the first technical concept I've seen in ten years that actually drives alignment between IT and the businessWhich I heartily agree with and indeed in general the links are full of some pretty good advice. Oh and of course of bad advice like ESB is the start. The clue is, as Roy Walker would say, in the question.
The starting point for SOA, for Service Oriented Architecture?
That'll be the Services, the ones that deliver services to the business in the way it understands.
So to be really, really clear. The starting point for SOA is
The next up comes the architecture.