Hello! :) Aplogies in advance, I am currently procrastinating so naturally this reply is going to be longer than necessary. :D
***Before anything else, I would seriously and strongly recommend reading as much of first person narrations as possible. Start with juvenile fiction books if need be (like Percy Jackson) and consciously observe what the authors do, and how they do things differently. Taking mental or physical notes of "oh that's how they managed to describe this!" is an enormous help: think of it as adding new tools to your mental writing toolkit. Especially when it comes to describing actions, whether to write emotion or action first, etc. etc. in "good" ways, you will most probably learn most from seeing how others have done it before you. :)
That being said, as people above me have already responded lengthily of your questions, here are some more general ways to think about writing:
- It might be helpful to think of descriptions (be it actions, appearances, scenes) as the mental camera lens through which the reader will see the world. Describe things around what you want the reader to remember from what would be the equivalent of a scene from a movie: the flashing diamond on that lady's neck? Her dark blue stiletto heels as she slips out of them? Where is the imaginary camera shot focusing on, or lingering on for whatever significance there might be? (Especially for first person POVs, your 'camera lens' is additionally your character. What is your character focusing on, noting, or drawn to?)
- You can also approach writing descriptions like you would art styles: some artists have very big, rough strokes that paint an impression rather than all the details, some have their scenes drawn to the smallest detail, and others have mixtures of both. What kind of visual do you want to leave the reader with? You could choose to "paint" your backgrounds with any style you want, though a good general rule of thumb (in both art and writing!) is to have a good balance of what you emphasize and what you don't. Just like how artists use line thickness variation and save flashier, more glaring colors for the bits they want to highlight, you can think of your descriptions the same way, giving what is more important (to the plot, to that particular scene, or to the character) comparatively more detail or emphasis.
- Lastly, this is not a rule but another general practice: if you want to describe something about the location or the character without feeling like you're info-dumping, one way (a tool, if you will) you can use is incorporate action into that description. Have the character interact with it, have someone else mention it (because it somehow relates to their backstory, maybe), or include it into a part of the plot somehow. Sometimes this will create a whole new unplanned arc in the story (ahahahhahhah) that you may have to write because this makes you discover new things about some of your side characters, but it's still an option. Use sparingly, of course.
Oh, and for dialogue: I've heard it is helpful to go out in public (safely!!) and just let other people's conversations sort of wash over you, so you can hear how people speak in real life. Reading your dialogue out loud can help catch any awkwardness as well, and giving your characters distinct voices (not in a super over the top way-- more like how there are some people out there who use 'like' in their sentences constantly) is another generally good practice.
Also, as a general grammatical rule, every time a new character speaks, please press enter and put it on a new line. It makes it less confusing on who is talking. Unless it's for deliberate literary artistic whatever purposes, I'd say the number one rule should be that your writing should be understandable above everything else, so. :))
I don't know if this will help, but ah well. Good luck! And more importantly, have fun!