Preston said he's often asked to meet up with people interested in landing a job or internship.
"The thing that stands out the most for me in a positive way is someone who has done their homework about Deloitte and all the different services we offer," Preston told Business Insider. "They come in with a little bit of an education or an educated guess about who we are and what we do."
Failing to do so will sound some alarm bells.
"If you ramble and start to talk about services or things we don't even do or offer then obviously I'm not as interested," he said. "And some people do that. They have a perception of who we are and what we do but it's not very well-defined."
If you're going to interview at a firm like Deloitte — which offers a wide range of services from consulting to auditing to enterprise risk management — it's best to make sure you know what they're all about.
Otherwise, you could end up sabotaging yourself in an interview or preliminary conversation.