You're asking about the first scene, correct?
The core of his deceit is that he feels one thing and expresses another. Therefore, start with the very first lines, when he is alone and describing what he's saying. Imagine him lingering over the poison of his complaints and spitting the lines out. He's jealous. He's angry. He's spiteful—and some of this comes from his body, and how he sees it. He describes himself " Deform'd, unfinish'd, sent before my time"; he was born prematurely and with disfigurements, and so hates everyone who is good looking. Therefore, the first deceit is that he is ever happy with others. Imagine him boiling with anger, and then slipping on a smiling mask.
His plans to do so are stated here:
"And therefore,--since I cannot prove a lover,
To entertain these fair well-spoken days,--
I am determined to prove a villain,"
After that, he lays plans to deceive people. One way is through spreading a false prophecy; another is to show sympathy for Clarence once it works out. A third is to blame Lady Grey; a fourth is to shift stories for Brakenbury, telling him "We speak no treason, man." So, he sets up plans, he puts on a false face, he shifts stories for different people, and he flat out lies. His face and posture needs to shift each time he shifts tactics or stories.