It is just me but I think an interviwer should have the following-
1. Interest in the subject
2. completed prior research on the topic.
3 Knowledge of the person being interviwed-
4. Few preconceptions about what the interview should be- meaning enter with an open informed mind ready to synthesize new or more detail on known info...
If you are going to interview any politician get your hip waders on If your interviewing Lewis Black- he may get excited and use coarse language....