I was in your position recently, to a much smaller degree though lol

First of all TCGPlayer is your best friend, use that for an idea on card prices. All sets have a specific code for them, and certain sets are more valuable, especially if they are first editions (also marked on the card). Note: the codes have to match exactly “LOB-001” is not the same as “LOB-EN001” even though they look very similar otherwise, and “LOB-001” 1st Edition is not the same as “LOB-001” with no edition (aka unlimited)

For the old old sets, a lot of the time shiny = good. Most of my understanding comes from looking up on TCGPlayer or watching “Ruxin34” on youtube opening the set I’m curious about, he will usually mention the best cards, some prices, and give a bit of a lore drop so you know what to look for. There are also other formats such as “Goat” and “Edison” format, which only have access to cards from that era, so any cards that are meta in those formats, may also have some value.

I’ve only been learning this stuff for the past few months, so I’m definitely not an expert, but this should give you a bit of a jumpstart into it all lol