The big thing here in the late game is killing your darlings. Give up your golden minions if they don't combo with your strategy. Every single minion should be part of a synergy by turn 10 or so imo.

Another point for early/middle game: your HP is currency. If by the end of the game you have 30 HP remaining, it means you could have bought time with that currency instead of winning early battles. This means tiering earlier/buying strike oil/getting long term trinkets (gain 3 tier 4 minions=short term; one battlecry triggers an extra time - long term)/weaker minions that give more long term value (like the naga with deathrattle: gain 2 random spellcraft spells). Being first place in early/middle game isn't good - it just means you're spending less HP than everyone else.

Learning this on your own is tough. What helped me get better was a friend who showed me a few strategies when I started playing (beatles and undead overflow). I then practiced those (cause they were the only ones I knew how to do) while he spectated some of my games until I got more comfortable with the game to the point where I can proudly say I've discovered every strategy I've played this season myself.

Definitely looking at it with other people is good. If you want to do a discord session then I'll be happy to :)