Think carefully in advance about what criteria are important to you. Courtesy and mutual sympathy are, of course, the most important. But also, points like diet, hobbies, and allergies matter. A vegan person might not fit with meat lovers, a couch potato might not fit with a sporty family, and someone with a dog allergy may not fit with a Golden Retriever in the household. Write down everything that matters, clearly state your expectations, and communicate thoroughly with each other, ideally through a video call.
Tip
Use professional agencies for matching, especially those specializing in the Au-pair's home countries. A helpful search tool for finding agencies can be found on the website au-pair-agenturen.de.