After nearly thirty years of performing and teaching voice-overs, I've come to categorize students and performers into four types:  Fighters, Flighters, Freezers, and Doers.  The first three types react to direction the way animals respond to threats.  Doers feel safe and perform with ease.
 

So, what kind of performer are you?  
 

FIGHT:  These are the "hard brained" actors.  Rather than accepting direction, they fight back and defend their choices.  They tend to beat themselves up for not having implemented the directorial choice on their own and try to second-guess the next direction.  This creates a tephelon effect.  Direction is given but it bounces off the performer and doesn't stick because the actor is busy thinking ahead and can't listen and absorb the information. 
 

FLIGHT:  When starting a job, these actors find excuses to leave the booth to get water or do other things that should have been taken care of prior to entering the recording area.  When direction is given, they often adjust the paper or stand, as if that's the problem.  They also have a tendency to want to finish the job and leave the booth as quickly as possible rather than enjoying the recording experience.  Rather than wanting to be in the booth, they want to be out of it.  Because of that, they often have a tendency to talk too fast.

FREEZE:  Like a deer in the headlights, these performers start with a glazed look on their face, stiff body position, and bewilderment of what to do.  Difficult words or lack of understanding of the script stop them in their tracks. Once the body is warmed up and blood and oxygen start circulating again, they gradually gain trust and confidence in themselves. 
 

DOERS:  These people feel comfortable in front of a mic.  They enjoy the challenge of each job and the expectation of a new one.  Their brains are "soft" and easy to direct as they embrace each new possibility and performance nuance.
 

Now, go  figure out what kind of performer you are.  Which type may depend on the type of job.  You may be a Doer in commercials and a Fighter in narration.  Learn to recognize these behaviors so you can deliver the best job in the least amount of time.  Keep your mind and body open and ready for work.