I was wondering if you could go into how you describe emotion in first person. In other words, how, without making your MC seem too self aware (unless this is their character) how you describe their physical response to things and then their emotional and mental response all staying in your MC's voice. I find that I'm running low on creativity for describing things like fear with sweat pouring down their face, or hands trembling, etc.
When describing emotions, you do the same things as any other description. You put yourself in your POV's shoes and describe what they feel and see and do. Instead of saying "Bob was scared," you'd show the results and outward signs of that fear. As the above says, the pouring sweat, the shaking hands and whatnot. But as our commenter also noticed, is that there are only so many words to describe things, and it can get repetitious.
The trick is to not overuse them.
If the emotion needs to be carried over a long scene, I like to space out my physical details so the reader can see the POV is feeling X, and then have little reminders as the scene unfolds that the emotion hasn't changed. If it's fear, they might start out with a racing heart, get the shakes later, wipe sweat from their brow after that. I usually won't have them feel all three at once unless the scene calls for it. Like if they're having a stressful "holy cow" breakdown moment after the fact.
I'll also look at the more subtle ways to show fear. Folks act differently when they're scared. Their reactions and thoughts will reflect that fear. They might constantly look around, or jump at sounds, question everyone they see and worry they're coming after them. Whatever fits your POV's mindset at that moment. They might grab a weapon and hold it tight, or put their back to a wall. They might pull their hair forward and hide behind it so none can see their face.
They might also think about the stakes or what they have to lose. Worrying about being thrown in jail can show fear just as well as shaky hands. They might even talk to themselves. Nya does this when I want an emotion to be right there on the surface. I'll give her urgent thoughts in first person italics: Don't see me, please don't see me.
If you mix all of these things together, you can space out the emotional details so you're not heaping them on the reader at once. Readers are smart, and they can figure out an emotion when they see it. And if you save some details, then it gives you the freedom to do a little more if the emotions gets stronger later.
A fun trick on that... chances are if the emotion gets stronger it's because the stakes have gone up in some way. This is a great time to use internalization or even dialog to show what the POV is thinking about. Make that emotion personal to them and not just an external feeling, and that'll help tweak those emotional stakes as well as the external stakes.
The second part of the question was how to do it without making your MC seem too self aware. That's much easier to do, actually, because as long as you don't write them noticing they're scared or reflecting on their emotions, they're just feeling them.
For example, you wouldn't want your POV to say something like...
I wiped the sweat from my brow, fear from my narrow escape coursing through my veins.
Aside from being a bad sentence, your POV probably isn't going to be thinking about what's coursing through their veins or why it's doing it. People just don't think about themselves in this fashion. They don't narrate their own life. It would be more like...
Sweat dripped into my eyes and I wiped my face on my shirt. I got away. I can't believe I got away. I stumbled to a bench and sat down, my trembling legs barely getting me there.
They'll notice how they feel, what they're thinking, how their body is reacting. It's looking outward from their skin, not inward at their skin. You don't want to explain why, you want to give enough clues so the reader can easily surmise the why. "Oh, she must be scared."
Sometimes it's spotting those cliches or word packages. (a word package is a combination of words commonly used, but haven't fallen to cliche status. Like "abject poverty" "general consensus" and "sweat from my brow"). We see them so often they slip in there without us even noticing. But they're placeholder words, relying on a cultural understanding of the phrase and not actual showing of the meaning behind that phrase if that makes sense.
Although the question specifies first person, all this applies to both first and third person POVs. Just like show don't tell, if you can avoid explaining why to a reader, and just show the results of that why, you'll paint a picture they can understand that puts them right in the action. Let the reader figure out why by what they see on the page.