Follow one piece of information
Pick a common business event, such as a new order. Map where the information starts, who uses it and where it gets copied or re-entered. The aim is to understand the workflow before choosing a solution.
Give every handoff an owner
An integration needs more than a connection between systems. Decide who owns the underlying information, who can change it and what should happen if a transfer fails.
Start with a bounded use case
A well-defined first phase is easier to test. Specify the systems involved, the information to exchange and the conditions that will count as a successful handover.
Plan for everyday operation
Include access control, error handling, documentation and support in the conversation. A useful implementation should leave the people running it with a clear understanding of what happens next.
A general business perspective, not project-specific advice. Requirements should be assessed for your product, market and circumstances.
Talk through your requirements