Note that doing one pleasant activity often leads to another. For example, if you go for a walk, you may meet someone. Then you may decide to organize an activity with that person. That evening you may have a helpful thought about what you achieved earlier. Such a helpful thought may then encourage you to go for a walk again.
When we feel sad or anxious, we tend to avoid doing pleasant activities with other people. Yet it is often social interactions that make us feel better.
Even when life is stressful, you have the power to choose to do certain pleasant activities. In this way, you can change your mood and a small part of your life, one activity at a time.