Your set point is the average mood you settle into on a daily basis with regard to different subjects. You often have different set points regarding different subjects, such as your work, or your relationships, or money, etc.
When you observe what is, you have a thought in response to it. Every thought creates a feeling response. The Law of Attraction draws thoughts to you which are a vibrational match, so once you focus on a thought that feels overwhelming, for instance, more thoughts come to mind which match that overwhelmed thought. Then Law of Attraction brings you situations which add to your feeling of overwhelment.
When you think about a subject, such as work, the way you chronically feel about it is your set point.
You could be frustrated about work, overwhelmed about money, discouraged about your body, worried about your environment, and appreciative of your relationship.
When you realize that how you feel is entirely in response to what you are thinking, you then know that your mood is entirely under your control.
When you also realize that Law of Attraction is responding to your habits of thought, you appreciate the benefit of thinking thoughts that feel better.
When you have a negative emotion, you know you just had a thought that triggered the negative emotion. Raising your set point is as simple as intentionally thinking thoughts that feel better. When you think a thought that feels better, the physical response is that of relief. When you have achieved relief, even if only a little bit, and you know you did it on purpose, you have raised your vibrational frequency.
As you practice the simple act of focusing on a thought that feels better over and over again, each time you find yourself feeling bad, you will raise your set points permanently.
Then Law of Attraction draws to you situations and events and thoughts that match your new, higher, better-feeling set point.
See The Vibrational Scale to understand different emotions and where the are in frequency, from highest to lowest. See Tools to find ways to raise your set point.