The basic tenet of a human mind is that it cannot be kept uniformly stable. The neurochemicals and our affect work in a way that makes us reactive to various situations.
At the same time, it is possible to practice a way to keep it relatively stable through crisis and various day to day challenges. The following tricks may help:
1. Deep, slow and conscious breathing, especially when one feels angry or anxious.
2. Daily meditation of a very basic kind for about 5-10 minutes.
3. Trying to recall a blissful, serene and happy moment of ones life.
4. Compartmentalization: Focus on the job at hand and shut off everything else
5. Staying away from all stimulant rich food and drinks ( that includes alcoholic ones); Especially during the time when you require your mind to be rock steady.
Give it a try for 10 days.