1. External dialogue—what they say out loud and how they say it
2. Internal dialogue—what they are thinking
3. Physical reactions—jumps, yelps
4. Involuntary reactions —heart beats, tingles
5. State of mind—can't think of nothing else, etc
The more actions and reactions you can include (to a point) the more your reader will be involved with your character.
Focus on one of the seven universal emotions: hate, disgust, fear, happiness, anger, grief, surprise
Emotional responses must be believable: not constant over or under reacting.
If you struggle with showing emotion in your writing, try some of the tips above! Good luck.