This may be a very tone deaf thing to say, but what really helps me is to just tell myself I am happy. It's certainly not fool-proof when faced with genuine problems, but I often find myself unhappy or annoyed for no particular reason. In those moments I just tell myself I have everything I need and life is great, and then it just feels better.

That said all the findings that these studies seem to gravitate towards like close relationships also align with my experiences as being powerful effectors.