This isn't a permanent solution, nor should you want one (hopefully) but this well help mask emotions.

You can conjure up certain memories that make you feel a certain way to counteract what you're feeling in the moment. Typically the "opposite" works.

Sad about something? Think about one of your happiest moments.

Incredibly mad but don't want to lash out? Remember a time when you felt peaceful.

This helps me a lot.

The most effective method for not showing when you're upset specifically for me is internally deciding, almost reciting, "I don't care what you think about me anymore."

Also look up some Bene Gesserit mantras, lol.