To imagine happiness you should not fall into the trap of imagining how things should be in order for you to be happy. Don’t think that you will be happy when you have the car you want, the house you want, the friends and relationships you want, just imagine being happy with what you have now. There is something within what you have now that is sustaining you and you can find happiness there. If you can’t imagine finding happiness where you are now, it will not be easy to find it as your circumstances change.
If you need help imagining happiness, remember happiness. Remember the most recent time you felt happy and the time before that. Remember the last time you felt generally happy. Don’t imagine that your circumstances were making you happy. It was all you. Imagine happiness and you will feel happy.