Failing to plan, as we know from Zen masters and MBA lecturers, is planning for failure. So when things go off the tracks with networks, servers, or your data, you need to have a plan, even if it's super-basic or seems gratuitous. Some back-of-the-envelope notes won't do the trick, nor will trying to recall hazy remnants of conversation from that night you and a coworker discussed incident response over a couple beers.
The middle of a DDoS attack or ransomware infection is not the time to be talking about divisions of labor or who should do what, crisis communications experts remind us, and they're right. Have an incident response plan, even if you don't follow it to the letter, or are forced to improvise more pieces of it than you'd like. You can minimize the improvisation and come out the other side in better shape if your incident response plan incorporates many of these steps. You can also recover more quickly and get on with the business of serving customers and making money.