Work on your self-control
The first thing you need to do in order to be emotionally numb is to gain control over your senses and body. Anger is basically a sense of heightened frustration and is only expressed when you lose control and patience.
Similarly, even if you are extremely sad, it takes self-control and resilience to remain calm and keep on moving ahead despite any hardships. In essence, controlling your emotions is about self-control and you need to start working on improving it.
You need to practice composure and work on your patience if you intend to improve it. This means whenever you are faced with a situation that tests your resolve or evokes emotions, you need to remind yourself of what you're aiming for, and remain in control.
Deep breaths, a glass of water and sitting down can all help you deal with stress and anger issues.
Stop expecting things
Emotions are often a result of expectations, especially when they're not met. The best way to be in control of your emotions is to stop expecting things from people. It's good if someone helps you or benefits you in any way, but you can't expect it as a right.
The key here is to be independent of such triggers around you which can evoke a state of emotional distress.
Take things slow
Emotional issues are often a result of shock. If you get unexpected news suddenly, you might feel you are unable to stem the tide of emotions that follow. The solution to this is to take things slow, allowing them time to sink in and dilute them so that they don't affect you fully.
Don't get attached with people
If you have a naturally friendly disposition, you're going to have trouble with this. People who get attached to others quickly often end up facing disappointment and consequently emotional issues. The best way to retain control of yourself and be emotionally numb is to not get attached to anyone.