A Harvard negotiation expert says too many people skip a crucial step when preparing to ask for a raise

If you've ever tried to approach your boss for a raise, you know how your tongue can turn to cotton in your mouth and your pounding heart can drown out the once-rational thoughts in your head.

That's why it helps to spend a few days before the conversation rehearsing exactly what you're going to say with a trusted friend or colleague.

Unfortunately, preparing for a salary negotiation is hardly so simple. There's another, considerably harder step that can boost your chances of success.

Business Insider recently sat down with Daniel Shapiro, founder and director of the Harvard International Negotiation Program, and author of "Negotiating the Nonnegotiable." He told us that it can be incredibly helpful to play the role of your boss while your friend or colleague plays you.

"Really emotionally take on that role," Shapiro said. "How are you feeling? Do you feel attacked? Do you feel defensive? Do you feel like this idiot did no preparation in terms of coming in and asking you for the raise?"

Once you take on the boss's thoughts and emotions, Shapiro said you can further tailor your strategy (as the employee, in real life) "so that the boss can most effectively hear what you're saying."

 Shapiro remembered using a similar strategy to help an acquaintance with his upcoming performance review. The man's boss could be harsh and in years past, he had left the reviews nearly in tears.

Shapiro encouraged the man to appreciate his boss and build some rapport by seeing the interaction from his boss's perspective. As it turned out, the boss was reviewing 40 people on the floor.

"Imagine what that must feel like to be sitting in that seat, being the demon, the devil to 40 different people," Shapiro remembers telling the man.

Sure enough, when the man walked into his review, he told his boss he'd been thinking about how difficult it must be to evaluate 40 people in a row. His boss agreed - and the review went more smoothly than ever before.

"Your boss isn't just a little robot, a machine that's going to press yes or no," Shapiro said. "Your boss has feelings; your boss has institutional constraints."

Whether you're heading into your annual review or a salary negotiation, Shapiro said "the more you can understand what those [feelings and constraints] are, the more power you have as a negotiator."