In everyday life one should develop friendliness or metta towards oneself and others. And if in your daily life you see people who are suffering, make it a point to do something for them. Then you are practising karuna. Sometimes there is a small thing, a little thing, that you can do in such a situation, just some little act of kindness. With this you develop an openness to the needs of others.
The quality of mudita is to rejoice in your own goodness. To rejoice over our own happiness is something we don’t generally do, we simply neglect that. Even more difficult is to rejoice in the happiness of other people. When others are suffering it might be easy to help them. But when they are happy, for us to really experience happiness for them is not so easy. But it is worthwhile trying because it can give more happiness to ourselves. When your own meditation is not going well and you hear that someone else’s meditation is going well, can you really be happy then?
The quality that is needed for this is to have a non-reactive mind. In fact this is one of the qualities that we are developing in meditation, upekha. When we are sitting, whatever happens within us, we learn to observe it with a mind that is non-reactive. And when things are happening externally, like noises and disturbances, again we can relate to them without reacting.