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.
Took me 20 years to figure this out and Im still learning.
It was actually Ralph who turned me on to these issues. He told me that he regularly uses a “pink label” ELO first pressing at shows.
He also told me to pay attention to the codes stamped into the run out groves. That they list the early or first pressings. I think that there is a indication by the number “1” within these stamps. But I don’t exactly understand where to look and exactly what to look for.
Charles, I did get a couple of Better-Records Hot Stampers. First I got a Super Hot Stamper. True, the vocal was clean an nice but the accompaniment was as usual. I was not impressed and sent it back.
Thinking that it must be the lower level Super and not White, I got a White Hot Stamper. A symphonic work, it was so offensive, I could not listen to the B side! I also returned it. Now I have cold feet and will not spend another $199+ again. I do imagine that your experiences are very “White Hot”. It is a lot of money for 40 minutes of hot sound. I have a lot of old, so so, recordings but find that I usually can enjoy the performance and live with the sound quality. I do find that I most enjoy the 180 gram remasters. 
Just use for every record if you want to know how many pressings made, first in the list is 1st press
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.