After almost 5 years of playing, I finally hit Master tier. I've learned quite a bit and here are some of the lessons I've learned from playing for so long.
(first sentence or two of each paragraph is the tl;dr for each point)
You know statistics? Throw those out the window. If you can conceptualize and get a good feel for the game, that's going to be 100x more valuable than just knowing statistics, especially once you hit D3. Statistics are only really relevant in low elos when dealing with the most extreme fringe cases (never forget 60% winrate WW preseason 5) or you're trying to find the biggest noobstomper or trying to analyze player behavior. For example, ASol has the highest winrate curve of any champion. It is appropriate to say that he's probably the best one trick champion. It's not appropriate to say, "This champion has a 47% winrate, thus they're not viable." Champions are viable or unviable for many reasons and you can get a feel for them in game.
Everyone makes mistakes. Tons of them. Even in lane there are ways to move properly, places to be to mitigate harass, and options to control the wave/last hit. Challenger players make tons of mistakes in the laning phase. What do you think that's going to say about Silver/Gold players? It's better to minimize mistakes than maximize plays.
It's better to play with your team than make the correct play. If you know your team shouldn't fight something, but you think you can turn the fight, it's generally better to be there and turn the fight than to say, "Hopefully they won't engage while I splitpush." Generally. There are exceptions to this rule don't try disprove it by saying "lul Tryndamere" that shit's obnoxious.
In low elo, champions counter champions by countering their kit. In high elo, champions counter champions by countering how their kit interacts with minions.
Building on the previous point, the biggest trait I see people don't practice is lane manipulation (pushing, shoving, freezing) into macroplay. Having a good knowledge of how your champion should play against the enemy will give you a better feel for the game than practicing the same champ 20 games until you have good reactions and mechanics.
Speaking of which, I have garbage mechanics. My secret is I look at all the options an enemy has, and think, "I can do a, b, and c and he can only respond with x and y because z will get him punished. If I take option b he'll use y and so be prepared to counter that." It's how you consistently land skillshots, predict flashes, and outmacro your opponents most easily. For example, if I'm playing against Kha'Zix as TF I say, "as soon as the teamifght breaks out I move toward my team, wait a few seconds, and ult so that Kha'Zix, who is probably invisible and about to jump on them from his flank, gets spotted. Then I cut him off, we get the pick, and we win the fight."
Be strong mental. I can't stress how important it is to stay active and take care of yourself. I play 2 games a day, tops. My usual routine is almost not at all until the weekend, during which I splurge. My priorities are food > school > sleep > exercise > League. If you're not in a healthy mindset you're not going to perform as well. Maybe play Fortnite or PUBG after a game that gets you particularly tilted.
Sometimes your top laner walks into Cassiopeia at level 1 and instead of admitting fault he says the solution is to buff BC melee champs.
Lastly, honestly when I first got on GD years ago I thought, "Wow these people are so smart and articulate." Now I see essentially the same posts and it's a lot easier to see the flaws or gaps in logic. People just aren't as correct or smart as they think they are. Please take what they say with a grain of salt.
Not gonna lie, it's pretty bittering. There comes a point where you see the same people over and over again. While there are some really "bro" players out there, there's also some really toxic players who you just don't enjoy being around because they consistently rage, flame, etc. and have no intention of real personal growth.
Generally, low elo players have 2 ways to act toward you; they want to take you down or put you on a pedestal.
Gameplay is pretty guilty of aggressive belligerence. A lot of them seem determined to prove you wrong under any and all circumstances, which seems pretty easy to do when the concepts that high elo players talk about are so abstract they look crazy. It's personally frustrating because I can talk about something like lane priority or, "you need to back at the 5:30 mark as Viktor" and people will look at you like you're an alien because they haven't studied up on those concepts or why they're important. So words tend to fall on deaf ears and people shut you out since, "Zed is permabanned so he must be a good champion." which has been going on a couple months now when in reality he wasn't really super good until maybe this patch or the one before (8.9). Again it's about statistics vs. meta/champion feel and it was very easy to scale up vs. Zed and play safe until you could afk waveclear, and that's what made him a bad champion. See what I said earlier about countering champions vs. countering minion interactions.
Oh, and don't forget the people on Boards who post, "screw high elo. 90% of the playerbase is below plat. Balance around us." I played hard to get here and I put in a lot more effort than most people. It's not fair to guys like me, scarra, qtpie, etc. who put in more effort to learning the game if you completely ignore how far we've come. Ya know?
Same thing in normal games. I play almost only ranked now because if you play normals, the games are super low quality. You get 1v3 camped, people base their entire strategy around taking you down instead of playing the game out right and when I want to learn new champions it doesn't help I have an almost unrealistic situation where I've got a ton of people ganking me every 20-30 seconds. Like I said, determined to take you down under all circumstances. It's not fun.
Blind admiration seems like a perk but it just gets obnoxious. I really just want to play video and hang out with friends or enjoyable people who also enjoy the game. The problem is a lot of your lower elo friends start looking at you kinda differently. I had one guy consistently pressure me to play ranked games with him on a smurf because he wanted free wins. You also get a bunch of people who just add you for attention, validation, or help grinding ranked (it's significantly worse if you're a streamer). You get a lot of players that are just super inconsiderate and treat you like a commodity. Yes, that includes e-girls (of which I've got none. Gotta be a recognized face first).
So yeah, that's pretty much the full experience. Overall as a gaming experience, it's pretty good. I'd say if you want a satisfying League experience definitely go for the top. People still goon quite a bit it's just not as pronounced.
In terms of player interaction, it can be a bit obnoxious. If you take anything away from this, it's that we're people too we just put too much of our free time into a game. Don't act like we're aliens. We get enough of that from families when we leave our room for the first time that week.