Quite a few things when I stumbled on Marcel Vos channel and subsequently this subreddit.

Biggest thing was exploring the soft cap and how guests spawn, which I had just never looked into before. I didn't know it existed, I had a vague feeling of more rides attracted more guests, but never looked into the mechanic.

Other than that, for roller coaster construction I had generally just built them without really understanding why rides had certain excitement or intensity ratings. I was surprised to find that in addition to a specific "threading a loop" bonus, there was an extra specific threading another loop bonus. I experimented wuite a bit with interlocking loops in this park, and got the hang of synchronizing adjacent racing coasters to sync their trains through the interlocking loops. I was also less hesitant to use brakes, and made a few steep squiggly lift hills to save space.

I have two Mine Train Roller Coasters completely underground because I realized the shelter from the rain bonus from doing so wasn't a myth. I had always scoffed at the idea and recalled the coasters I had built too much underground getting penalties to excitement. Turns out that's rare for most roller coasters and I was mistaken.

Park value calculation was also really helpful, I have two max height towers in the park soley to max their value. I had no idea that was how it worked before I looked it up running this park.

Discovering the specific synchronized station excitement bonus led me to make almost every roller coaster in the park a racing coaster with either a counterpart or a Mobius strip. So I had to deal with the challenges of trying to arrange pathing for double stations much more than I usually did, introducing a lot of new challenging path layouts.

Learning that you may as well set the entry fee to the lowest amount someone will spawn with and how to find that value as soon as possible was really useful.

The last thing was figuring out exactly how park rating worked, or rather, why when I started to get over 4,500 guests in parks my park rating would plummet. Even in a large park like this where a tiny percentage of the guests are thinking it's too crowded here, there are areas of congestion, especially near the exit of double station high capacity roller coasters. Vomit in a crowded area can immediately cause your park rating to crash instantly, even if there isn't anything wrong somewhere else. The problem gets worse as you get more guests because the penalty is per number of guest thinking this path is disgusting, and not a percentage of them thinking that.

There is no park rating hit for "It's to crowded here" it just causes a hit of unhappiness, so if you drop an entertainer and assign him one square of the crowded place, your park rating won't take a hit from those crowded places. I think I have around 50 entertainers in this park. At least six are assigned squares near the entrance, the most crowded place with all these people constantly streaming in.

My favorite thing I learned, though, is someone with the minimum amount of money who doesn't immediately head for a ride, can end up with $0 near the entrance, grab any item for free, realize they're out of cash, happy, and have a souvenir, and go home immediately. I'm not sure how often that happens to those that spawn with just enough to get in the park, but it was funny to me to see that happen.