To get the most out of the relationship between you, whose role is as an instructional designer and your subject matter expert. There are a few tips you need to know and two of them as follows:
Show your SMEs the value. Before working together with the, you need to give them an assurance that their services will be valuable. To do so, you can show them the estimation for the finished product and the result which will achieve from the project that they will be able to understand exactly how their contributions in the plan will make an impact.
Build a relationship. As you might already know that the relationship between you and them could be a difficult one, yet you might still need their services in the future. Hence, you need to make sure that you are on good term with each of the expert that you will not have a hard time connecting with them when you need them again.