@Deezel177 made some great points and many of my own are just footnotes or alternate ways of saying the same thing. Following is how I would frame advice to folks new to the portable space based on my own experiences as a "noob" just a few years ago (2019 seems like a different world ago, in more ways than one).
1) First and foremost for me is:
don't let others do your thinking and listening for you. This hobby is full of people-- some of whom are sincere, others not so much-- who want to tell you what to like, what not to like, what is worth the money, what is not, what good sound is, what it isn't, what is snake oil, what is not, and so on and on. In my experience the greater the extent to which one is able to follow their own inclinations, desires and convictions and not get caught up in what everyone else is doing and saying...then greater will be the degree of their own satisfaction in this hobby. This is not to say that we shouldn't take advice from or consult others...far from it. It's just that I have found-- even with people I tend to jive with most of the time-- that there will be times when we just flat-out disagree or hear things differently. The most fundamental rule in this hobby for me is:
let thine own ears be the judge.
2)
Youtubers, high profile reviewers and influencers are often some of the worst people to listen to for advice. Sorry but it's true. The more someone tries to posture that they're just "keeping it real" or "telling it like it is" the greater the odds are that they're just a shill after clicks and likes beholden to whoever is sponsoring them. There are exceptions, of course...but exceptions they are for the most part in my experience.
3)
Listen to anything and everything when you are just getting started. You have no idea what your ideal sound will be and no amount of consulting others will reveal this to you. Remember: One must taste the fruit to know the flavor.
4)
Don't underestimate the value of sources and synergy. This is a lesson I am still learning to this day. In my experience good synergy can add a kilobuck or two to the perceived "value" of your setup.
5) When getting started
scour the length and breadth of the land to get a sense where everyone is coming from. There are all kinds of ideologies and temperaments out there-- what works for some may not work for others, and where some fit in, others may not. I don't personally relate to the audio nihilist and graph worshiping crowd-- but many do. Perhaps that is your ticket to finding meaning in this hobby...and if it is, jump right in. The main point-- don't fixate on or limit yourself to one particular community, especially at first, as often these can be echo chambers that can limit your perspective or keep you from experiencing something that could be right up your alley.
6)
Find the price tier you are most comfortable with and which gives you the most satisfaction-- and focus on that. You might not need the summit of the summit priced IEMs to hit your particular groove. Similarly, avoid the fantasy that out there somewhere deep within the audio abyss is some mythical $50 IEM that will render all flagships obsolete. While it's not unversally true, it's overwhelmingly the case that spending more will result in better gear and more satisfaction. I have personally found the sweet spot to be about ~$1500...but it might be different for others.
7)
FOMO is a thing. There is no sense complaining about this, it isn't going to go away, so we may as well learn to process it. This hobby depends on a relatively constant stream of new releases. Every now and again many of us-- even vets-- get super excited about some new release, quickly proclaiming it the greatest thing ever, prompting everyone else to succumb to that most pernicious of curses in this hobby-- curiosity-- only for the hype to die down sometime not too much later and the thing in question fades into relative obscurity before too long.
8)
If it's not doing it for you, let it go. This can be a hard one. We've all been there-- over the moon hyping the sh1t out of some new release, or jumping on something that everyone is interested in...only to have this nagging voice at the back of your head telling you that it's not really doing it for you. Listen to that voice and move on-- your own personal satisfaction with what you have is the most important grail in this hobby inho.
9)
Don't be afraid to play the used market-- you don't need every new thing as soon as it comes out. One can save a lot of money and maximize their enjoyment by waiting a bit and picking up something on the used market for a great price after a time. One can hear a lot of great stuff at minimal cost by judiciously buying and selling used gear at a minimal loss. I did this early on and got to hear a lot of great stuff.
10)
If at all possible go to a CanJam or some other meet. Curiousity is the burning and driving force of this hobby. Hearing as much as you can at various meets or through tours will eliminate that curiousity which often prompts us to make poor choices around what to buy and it liberates us from the temptation of FOMO and the babel of everyone's hype and conflicting impressions.
In other news we're just about down to the last 24 hours to vote in the
Watercooler IEM of the year Survey so if you haven't voted yet and want to, now is the time.