The first question is: Is the relationship a partnership or a seconding or and involvement? It's important to understand the verbage and what is expected with each kind of relationship. In brief, I see the following distinctions:
-involvement - a casual working relationship with a common goal or project
- seconding- coming along and joining your talents, gifts and skills (and possibly some resources) to another ministry's goals and structure
- partnership - implies an equality to some extent in goals, vision, decision-making and effort (resources)
There are probably other kinds of relationships we are involved in within a broad continuum, but the first step in having a successful partnership is to define the terms and expectations on how the relationship is going to operate.