Hollow Knight is a solid contender for my favorite game, so good choice! I'm going to try to keep things spoiler-free as much as I can since a huge part of the experience is exploring and slowly unraveling things. Here's a list of (hopefully spoiler-free) tips that I think might help.
Not much will make sense at first.
Hollow Knight follows the Dark Souls school of lore: You don't get an exposition dump in the beginning giving you the whole background behind what's going on. It's perfectly fine to be confused about what you are doing and why. In fact, I'd say that's an intentional choice that winds up making a ton of sense after a certain point in the game.
Careful looking up info
Because of this fact and how long it's been out (as well as how popular it is), it's unfortunately very easy to spoil things. Be careful with that, and make sure to tag on "spoiler free" to any searches you do on the game.
It's difficult, but fair
You're likely going to die a lot, that's true. That being said, there aren't really any situations that I can think of where I had no way to avoid dying. The nice thing is, the game sort of sets itself up in a way that you (hopefully) learn different techniques over time, and the fact that it's a metroidvania means you get upgrades drip-fed to you, so you don't have a million things to try to learn at once. I'm not great at games nowadays, but I did still manage to beat the game. I never completed the boss rush stuff, but that's more because I've never been a huge fan of boss rushes in general.
It's methodical
You don't have a time limit during fights. Feel free to take your time learning an enemy's attacks; there are generally tells you can keep an eye out for so you can prepare to react appropriately. Don't be afraid to keep your distance as much as you can while in a fight.
Don't forget your Soul
Soul is the game's "magic" system, and it's a pretty big help in keeping you from dying. You recharge it a bit each time you hit an enemy, so as long as you're able to run in, hit an enemy, and get away without getting hit, you can recharge enough for another use. There are also generally minor enemies in each area that are relatively easy to deal with - these are basically prime candidates for recharging Soul if you're low.
Be sure to explore
There are going to be quite a few dead ends during your journey. These are usually places you just don't have the tools to deal with yet, so if it seems like you can't progress, try somewhere else and come back later! Another thing to keep in mind is you'll sometimes hear or see weird stuff on your journeys - it can be worth putting in some extra effort to see what the source is. Something that I would say is important for this is the map and quill you can buy in the shop in the first town. It updates when you sit down at a bench, so don't worry if it doesn't seem to "work" right away.
If you're having money troubles...
Grab the "Gathering Swarm" charm from the store in the first town, go sit on a bench, and equip it. It won't make your money problems disappear, but it'll help.
Enemy spawn mechanics
Enemies only respawn when you sit on a bench. Yes, that goes for the entire map. Yes, I have cleared a significant number of enemies across multiple zones without sitting on a bench and verified this (it was to help me finish a specific side quest). No, bosses will not respawn.
Hopefully this gives you a decent set of tips to get you started! I hope you enjoy your journey as much as I did when I played the first time!