My two cents
Always share the why
Service designers are usually people who like to understand why you expected something from them. You will get much better results, if you take a few minutes to share why you want them to help you with that.
Because service designers are used to try to understand the deep reasons why people care about something or why they hate something.
Let them speak directly with a few people.
Service designers are people's people. They have a deep sense of empathy. And a big part of their job is to interview people in order to understand what they like and what they hate about a service or the ways the service is done.
Therefore it's often important for a service designer that he can speak directly to the people who will benefit from his work or who will be impacted by it.
It won't be enough if you just tell him. People like this. But they might like to hear from the people directly.
Get used to sticky notes.
Many service designers like to work visually, especially with sticky notes. These can be digital or good old pieces of paper. It helps them to rearrange information and visualize complex things in a very quick and efficient way.
So when you collaborate with a service designer and he takes out sticky notes, it doesn't mean that he has no memory, but it means that he is now trying to understand and map all of what you're telling him. Which is a sign of deep interest.
Ask them questions.
Often service designers are people who are very curious and like to ask questions. And therefore they especially like when people ask them questions back. So whenever they use fancy words like prototyping, Service Blueprint. Don't hesitate to ask questions. They will love it.
Show them some qualitative data too.
Often service designers have a positive bias towards qualitative research. So if you have any qualitative research data, like interview notes, make sure to share it with your service designer. He will love it.