When a feeling or thought arises, your intention should not be to chase it away, hate it, worry about it, or be frightened by it. So what exactly should you be doing concerning such thoughts and feelings? Simply acknowledge their presence.
For example, when a feeling of sadness arises, immediately recognize it: "A feeling of sadness has just arisen in me." If the feeling of sadness continues, continue to recognize: "A feeling of sadness is still in me." If there is a thought like, "It's late but the neighbors are surely making a lot of noise," recognize that the thought has arisen. If the thought continues to exist, continue to recognize it. If a different feeling or thought arises, recognize it in the same manner.
The essential thing is not to let any feeling or thought arise without recognizing it in mindfulness, like a palace guard who is aware of every face that passes through the front corridor. If there are no feelings or thoughts present, then recognize that there are no feelings or thoughts present. Practicing like this is to become mindful of your feelings and thoughts. You will soon arrive at taking hold of your mind.