Tip 1 - Reference Reference
I always film my own reference when trying to recreate any emotion in a character. It's not easy acting in front of a camera, but running through the action over and over allows you to at least get a sense of how the character feels. Usually after 10 attempts or so I will have loosened up and managed to capture a decent take. Along with this video reference I will collect some other reference from YouTube or hero facial poses from Pinterest (which is great for animation reference). This gives me a great base to build on and enhance the performance however I want.
Tip 2 - Review
Get extra eyes on it... Usually when I've been working on a shot for a while I become blind to it. Step away and show people your progress. Although animation is a very subjective art and you may get a lot of "suggestions" most people can read emotion in a face very well and will be able to tell you if the one that you are trying to capture is coming through or not. Also, try just looking at some of the still frames and poses in the shot - is the emotion still coming through even without audio and movement? If so you're on the right track.