How do I make a character, who's kind of shy, show his emotions?

Writing really is the study of human beings and how they express 
themselves. Every opportunity you can - EXAMINE (like a being from 
another world) how the humans that surround you express the vast array 
of emotions that color our daily lives.

You’re right, some people are withheld - 
the merest lift of an eyebrow says volumes about what's going on in 
their heads. Other are like fireworks displays - about everything; 
love, hate, happiness, boredom it all gets colored with some 
incredible display of emotion. The films that affect us the most are 
the films where the writer has created a VISUAL language that relays 
even the tiniest detail of a characters INNER landscape (emotional 
landscape) to us, the audience.

So, give some thought to the multitude of NON VERBAL bits of 
communication that are peppered throughout your day... your child 
opens it's arms wide for a hug when you come home; but doesn't SAY 
anything. Your boss merely crooks a finger in your direction and 
disappears into her office. You know you've been summoned. At a chai 
shop, a handsome fellow merely meets your eyes over the lip of his 
cup, which mostly hides his smile of acknowledgment.... you TELL ME 
what that means!!

Start cataloging in your mind the various ways people SHOW 
us every day what they're thinking... instead of using words. Do this for a 
month and you will be on your way to understanding one of the key 
elements of screenwriting. Show - don't TELL what the characters are 
thinking.

I hope this helps. And I do wish you luck with your screenplay . Let me know when you’ve completed your script. I’d love to read your work!

Recently I particiapted in a 'cold reading' night and my script was critiqued by the resident judging panel.

The overall verdict was that I was a smart writer and the script had real promise but no heart. What does that mean?

First of all, congratulations are in order. #1 - You finished a script. #2 - You risked submitting it to a ‘cold read’. Wow, that’s fabulous.

For those unfamiliar with the term, a COLD READING is a gathering where a group of actors meet, are handed a script and within about 30 minutes start acting it out. Often, it’s just the opening act (or first 30 pages) of a feature script that’s read. And it’s one of the scariest rides on the planet and one of the most exhilarating! Hearing your words in an actors’ mouth is one of the BEST WAYS to gauge the effectiveness of your dialogue and pacing of your writing.

And as you found out, a cold reading can also reveal some of the weaknesses of your script that might have slipped by some of your other critiques. From the comments you received it sounds as if you were shanghaied by the LEFT side of your brain. As many of you know, who follow this screenwriting blog, I believe any really good story is a balancing act of RIGHT brain creativity and LEFT brain structure.

Really well-plotted thrillers and heist movies delight us with the mastery of the turns and twists of their plot. (LEFT BRAIN). But if they contain heart-wrenching scenes of loss or betrayal those deeply rooted emotional stories come from the RIGHT BRAIN. Right brain function is all about universality. (Jill Bolte Taylor’s fabulous, fabulous recorded TED talk - http://www.ted.com/index.php/talks/jill_bolte_taylor_s_powerful_stroke_of_insight.html ) gives a beautiful and passionate explanation of the relationship between the two brain hemispheres and creativity.

What’s probably missing in your piece is that moment (s) where the camera focuses on the protagonist and we get to SEE their pain/reaction/emotional response. We need emotional connection to the main character to actually care enough to plow through their story with them. EARLY on in your script give us an emotional LINK to your hero/heroine and then reinforce it several times throughout the story. Those emotional ties will keep us cheering your character on until the bitter or sweet finale of the film.

I hope this helps. And I do wish you luck with your rewrite. Let me know when you’ve completed your script. I’d love to read your work!