You know you have to bring up a difficult topic. In addition to thinking about the issue and the words you will choose when talking about it, it is important to think about when and where to have the discussion.
If you are going to your spouse about a problem (that you have with them), then it is best to go with the communication position in which they feel most comfortable. Since the discussion has the potential to put them on the defensive, you want to make it as easy for them as possible.
For some people, talking shoulder to shoulder is best. They may respond better to deep conversation while driving down the road or doing something together.
Others need to be face to face, looking at the other. It might mean going somewhere for coffee so that you can look at each other.
Some do better over food. Or walking side by side. Or sitting on a park bench near each other. Or by the beach or some other nature.
Choose when and where to have the conversation carefully – you want to make your partner most comfortable for an uncomfortable topic.