How do you know when an LP is a first or early pressing?

Being relatively new to analog, there has been a steep learning curve.
The latest important bit of knowledge has pointed me to the codes stamped in the runout groves, the labels and the sale listings. The questions are how to read the codes, and what to look for on the label and on the sale listings? For instance, a friend guided to to the “pink label” British Island Records pressings. Believe these are all first pressings and the original British. I bought a couple including Emerson, Lake and Palmer’s first album. A pretty good used one cost me $25 which I understand is a good price. I would like to find and buy more of these early, or first, pressings. I understand their sound quality is normally, or frequently, excellent.
A good example of this is the early Roxy Music records. The 1/2 speed remastered versions are worlds better than the originals.
I go with the country in which the recording was made. Roxy being a British band you really want the Brit originals.

The more transparent your system is the easier it is to hear the differences. Resolution is important- stuff that sounds distorted on lessor systems can simply be detail- that a proper system will bring out and reproduce instead of getting freaked out about it. A great example of this to me is on Nonsuch 'Bulgarian Village Music' which is a field recording and has a bit of power in the vocal regions... I've heard many systems freak out on that LP, but in fact its immaculately recorded and stunning on a highly resolved system.

Its a real treat when you find a gem and play it on a good system!
As Millercarbon said, the hot stampers from better records are great! One example of an original not sounding as good as a later reissue Is Miles Davis Kind of Blue. The original 6 eye Columbia is inferior in sound quality to the very early 70’s reissue on the Columbia red label.
OP, I can give you some examples what the numbers etched into the dead wax mean. Each record label has their own system.

Here’s an early 1st pressing of a Kate Bush album, the matrix number is:
YAX 5389-1
YAX 5390-1
The catalogue number and county of origin is included;
89 is side A, 90 is side B. The -1 means it’s the first production run on stamper #1.
The question is was this vinyl pressed early in the run when the stamper was new, or was it pressed late when the stamper was becoming worn and needed to be changed?
The only way I know of is to play it. There may be additional etched numbers which identify it. And the mastering engineer and record plant code may be scratched into the runout. A -2 may also be on a first pressing.

YAX 5389-4
YAX 5390-5
These are pressed later with a different stamper but may be of better SQ because they were at the beginning of the production run.

As stated earlier, the label is important in identifying early and late pressings. Record companies change the label for various reasons, eg, which country it’s released, reissue, early issue.

Steve Hoffman forum has lots of info on first issues and best quality pressings.

Discogs usually has all the info you need. The real fun starts when your buying records that Discogs doesn’t know about (yet)!
Mglik, I think that you are correct to be wary of ’hot stampers’. To my mind, the history of a record is a lot more important than its stamper: you know, what kind of blunt stylus was used to play it, if it was used as a dog’s frisby, and so on.

Let me tell you about something that you can control: how clean it is. Once you get into ultra-sonic record cleaning, you’ll never want to go back.

Good luck!