Every case is different and your first steps depend on what the issue is. Let’s say someone complains of a performance issue and gives you a packet capture. That’s all you know. Where do you start? I’d probably try to get more information than spend time looking for something that I don’t know what I’m looking for. But how are you going to get the reputation of a miracle worker if you don’t pull one out of the hat every now and then?
Here’s how I’d get started looking at a performance problem that I don’t know anything about.