Something is about to happen - something significant is going to happen that affects my character. What saying can I use to kinda forebode this? I want to a convey an impending sense of change, like for instance "take a deep breath". Dramatic, but not too dramatic
If the character knows this is happening, try making the actions reflect the characters reflect their emotion about what's going to happen.
What type of thing? And what viewpoint is used? (1st / 3rd / etc) And is it in dialogue or narration? The first thing that springs to mind is it's often important for an omniscient 3rd person narrator to avoid doing this e.g. with lines like "He could feel in his soul that something significant was about to happen.", which can come about from too much telling-not-showing, and can be difficult to fix. If it's in dialogue and it's that a supporting character is informing the MC that - for example - their long-lost mother is going to be arriving later that evening, then that's completely different. Someone has realistic knowledge of a pending event, and it's about finding what language they would naturally use to prepare the other person. There are so many possible situations that I think more information from the OP would be useful.
It's supposed to be 1st person. No dialogue. The context is that I am about to do something that will shape the course of my life (in this case, using a swingset, lol). It's supposed to be hyperbolic.
Yeah, there's definitely not enough context here for a proper input. If your story uses 1st person, I don't know how s/he could sense that something significant is coming her/his way that s/he could consciously react to the impending sense of change. I guess this is mostly why I prefer 3rd person limited.