Deception How-to: Acting

Acting is the combination of two innate traits: empathy and imagination.

Step 1: empathize with the person you want to portray yourself as.

Step 2: imagine how they would behave.

Step 3: copy your own imagination. 

Cheat: if you've seen it in person, you can check your work by comparing your imagination to your memory, and then copy your memory instead of the imagination.

There doesn't seem to be any training arc. Either you do the steps and it works immediately, or you can't and it doesn't.