Are they very formal? Friendly? Upbeat? Precise?
For example, if they're wearing a suit and tie in an extremely hot summer, and they're very well groomed and are they asking direct questions about your background with narrow eyes and folded arms, this gives me a tremendous amount of information about the kind of person they are, where their concerns may lie, and how to provide the kind of answers in a format they'll prefer and appreciate.
By training yourself to be aware of the person on the other side of the table, it's remarkable the detail and level of personalised information you can pick up. Of course, this is a skill and takes time to develop.
Article: "If the job seeker doesn’t take time to understand the company, and personalise their written and spoken message to the hiring manager at that company, it’s easy to see why the business might pass them over for candidates that offer more personalized communication."
Under "How do I personalise my message?", theres an example of customising your message on the fly in the interview.
In regards to actually applying for the job, there are 5 examples of customising your message to apply for the job.
The way I define the shotgun method, and why it's a flawed method, is that it's a simple process of copying and pasting your resume and cover letter with only the briefest of changes in the company name and the hiring manager's name (and sometimes people even forget to change these) - without any understanding or interest in the business itself, and the problems that it's trying to solve, both in general and with hiring you.