Use character traits to "show" your characters.
In particular, use the main attributes of the characters to show, rather than tell, the story. For example, if your character is "lazy", don't describe him as lazy. Instead have him speak and move and act in a lackadaisical way.
I know, nothing new here. This is stuff we have heard. But honestly, it is NOT something I do as well as I could.
To help "teach" the point, Amy had us make a list of our primary and secondary characters in a current WiP. We then had to come up with one or two words to describe the main attributes of the character. She suggested having this list written or printed where we could refer to it often as we revise our manuscripts.
Wow! What a powerful exercise. I have to say, this simple process has not only helped me maintain my characters voices in my current projects, but it has also really helped be zero in on my characters.
Here is a sample of my list for my current project, TRANSCEND:
Ien - submission, insecure
Erik - confident, dominating
Katherine - controlling, scared
Kiera - untouchable, free
James - loyal
Sister Anne - passively controlling, illusive
This list literally lives on a 3x5 card I pull out as I revise. It is a godsend, trust me.
Try it out for yourself and let me know what you discover.