TLDR; Groundstrokes and volleys from stronger opponents will crush you
I have recently started meeting much stronger opponents as I have climbed the ranking in Norway and hit top 100 after a few decent tournament results. Please note top 100 in Norway IS NOT the same as top 100 in other countries like Sweden, Netherlands etc. The number of players in Norway is still quite low so only reaching a few quarterfinals/semifinals in a 250 tournament is enough to get ranked top 100.
Regardless, I was finally feeling able to win a decent number of matches and potentially fight for the title in these 250 category tournaments in Norway. Unfortunately, due to lack of players, the past months I have placed in the 500 and even 1000 category tournaments, meeting some of the top players and top young talents in the country.
In these matches I have gotten destroyed 6-0 6-0 etc, and had a bit of a eye opener as to what really matters against better opponents. People here mention dealing with glass, tactics, improve overheads and so on but in my experience that is not the case.
For me, the biggest takeaway is to improve the most basic of shots. Groundstrokes and volleys. The quality of the groundstrokes from these better players are much better than what I am used to. The groundstrokes are coming fast, barely crossing the net height-wise and with slight topspin so it goes below the net immediately after crossing it. I have practiced volleys for hours and hours, but I can't use my practice against these groundstrokes because they are much different shots to volley - you don't have time for a full preparation and need to react fast, and often you hit the shot below the net. Without experience tackling these groundstrokes, your volleys will suffer and the opponents get a chance to take the net with a lob or chiquita CONSTANTLY.
Now on the flipside, the same is true - my groundstrokes in defense, which I have to say is one of my better shots and gives me a lot of opportunities against same level players, are too easy for these stronger opponents. For them they are attacking balls, or at the very least comfortable balls, completely opposite of my reaction to their groundstrokes. And their volleys are very good, they will successfully attack your groundstrokes and choke you in defense.
Of course, the better players have other qualities as well - they smash well, dropshots, passing shots, chiquitas are all in the mix. But for me the most important part is the basics. If you can't volley with high enough quality against their groundstrokes you will lose the net all the time. If your groundstrokes are not pressuring their volleys when you are defending, they will attack you more and more until you get crushed.
After losing the first round of a 1000 category tournament a few months ago I played the "plate" bracket and made it to the final and there I met Louis from Padelactico who played with one of Norways top young talents. My experience there was the same. They crushed us. Here is [his video](https://www.youtube.com/watch?v=yKAQFxUYuSM) from the tournament where meeting us is at the very end. Also my [full video](https://www.youtube.com/watch?v=Hq3PxT1E9dY) from the match if anyone is curious. I'm the leftie he mentions as "table tennis background with good hands" :P