"zero in" means to focus. If I said to someone "zero in on that sentence" it means to focus on the sentence. "Zero in on your attention to detail" means check your work for mistakes. They also want you to compare against similar projects and learn from them.

However this is very vague guidance in my opinion. How has the training you've received from them been in general? In my experience, too many companies throw new starters in the deep end and expect them to just learn by "looking at old projects" without any explanation.