Some days, the cause of my cloudy skies is simply cloudy thinking. For example, I often think that I can be happy if I only I manage my life just so. It doesn't work. My life cannot be managed. It may be different for you of course, but for me, life happens fast and sometimes it happens hard. Trying to manage it only leads to frustration or worse, but no matter where it leads, it never, ever turns out well.
The inner sun can be encouraged to come back out again on those cloudy interior days. The technique that works for me is consciously living life on the terms dictated by life rather than trying to live life on my terms. This means mindfully paying attention to what is really happening--not what I want to think is happening--and then acting on it.
After accepting the reality of the situation, I must then find my role in causing it--and I have a role in causing 99% of all things that happen in my life. Accepting and recognizing the part I've played will give me the opportunity to stop it and to step above it.
The process of making the sun shine again always includes gratitude. I may struggle with that but I can always start by remembering that there is always more right than wrong, more good than bad, in any given moment.
This process always works when I honestly work it. It may not bring joy everlasting but it will part the clouds and allow the sun to shine through. And that's enough. Some days it's enough just to make a shadow. Life is good and, as Louis Armstrong said, it's a beautiful world.