This practice is NOT about trying to pretend to yourself that you think or feel any different than you actually do feel and/or think. There's no pulling yourself up from your boot straps. That never works!
The key here is that you get really very self-honest and observe precisely how you are involved in making yourself unhappy (if you're doing any of that). When we realize how much we're involved in our own unhappiness (if we have any of that) we learn how to care for ouselves better and thus how to grow in happiness.
This is about choosing happiness by acknowledging the available choice. It is also about bringing joy to others by becoming joyfull.
Joy is always in you, if you will only notice it and give it your attention. Attention to this joy causes it to expand and to heal the hurt or broken places in ourselves.
I know, it sounds really weird to say "Joy is always in you". That seems especially ridiculous or absurd when one is feeling miserable! But I have found that joy really is always in me, and that it expands when I attend to it -- pay it attention. The only way to find out if this is true for you is to practice toward finding out.