I've found myself rather enjoying Valheim ever since I first picked it up, racking up a total of 300 hours in my time with the game. I've learned quite a bit since I started and I'm happy to share it!
Valheim is a game that, honestly speaking, doesn't do the best job of explaining itself. I spent a lot of time getting my butt kicked and learning from the experience, and I couldn't count how many hours I've spent reading about experiences, tips, and tricks from other players. Some things I've learned, however, are far more important than others.

Stamina is King
You need Stamina to do pretty much anything in Valheim. Running and jumping will slowly burn your Stamina, and bigger actions like chopping down a tree or blocking an enemy attack will burn greater amounts of Stamina.
It sounds like a fair enough system—until you run out of Stamina entirely and discover, much to your horror, that you are effectively helpless. Attempting to block will result in extra damage bleeding through. You can't run. You can't jump up to a ledge just two feet above you.
Heed my advice: manage your Stamina and you'll have a much easier time in the game. Don't let it run out in a dangerous area. Time your attacks carefully and don't needlessly run around in a fight. Patience (and conservation of energy) wins the day.

Planning Your Moves is the Key to Success
Valheim can certainly be brutal. Any veteran player with a few dozen hours can tell you about a nightmare scenario where they were trapped in a river or stuck on a mountain crevice while being relentlessly pursued by wolves. Many of these situations can be avoided simply by carefully planning your moves.
Take the game's second boss fight as an example. The Elder can prove to be a challenge—his ranged attacks can knock down trees, you can get trapped in an unfavorable position (like a circle of roots that attack you), and the Black Forest location means that a Troll could be just around the corner.
Plan your battle carefully, however, and it's an entirely different fight. Prepared fortifications or trenches can save you from his deadliest attacks. Chopping down all of the trees in the area keeps any of them from falling on your head. And best of all, killing enemies in Valheim typically means they won't spawn again for a good 15–20 minutes—so you can prevent that problem, too.
I've found extending this philosophy to the entire game makes it a lot easier, even if my plans don't always succeed. I was horrified to find that miniature stone walls I had built to block the fourth boss's attacks were turned into rubble with a single shot—but they still saved me from that one attack. The remaining rubble provided ample cover, too.

Valheim is Better with Friends
I started out playing Valheim solo before some friends picked up the game. I soon found myself playing on a shared server with my colleagues at TechRaptor, and boy is it a different experience.
Let me be clear: You can absolutely play Valheim solo. Some things may be more challenging without someone to back you up, but it's entirely doable. Bringing some friends along for the ride, however, can be a serious game changer.
Throughout the game, you'll need to cook up food, collect materials for crafting items and armor, build structures, and explore. You have to do all of those things by yourself in a solo game. Having some friends with you can change that dynamic to the benefit of everyone.
My multiplayer group has some people with particular quirks. One of them loves to explore and forage for items, and that makes it easier for the team to make meals and craft important meads and potions. Another has a knack for fortifications, giving us a staging area for exploring a new island or prepping for a boss fight. I'm personally great at organization and planning, so I've provided several storage and crafting areas to make it easy to sort everything.
Any one of us could do these things on our own, but working together plays to our strengths. I don't have to break the flow of building because someone has collected a few thousand Stone. I don't have to run out and get food because someone has cooked up 50 Turnip Stews overnight. And, of course, it's often much more fun to share the adventure with your friends.
After 300 hours, I'm more than happy to say that it was well worth the price I paid. Our multiplayer group has beaten all of the bosses, and I've tackled the first three bosses in a solo world. I probably have another one or two hundred hours in me at least—and that doesn't count the inevitable distraction of making some amazing new buildings.
That said, Valheim does feel like it's running out of content for me. I know the day is coming soon where every available challenge has been conquered, every corner of the realm explored, and every item crafted. That's OK. Valheim will simply slumber until the day arrives that there are more new things for me to enjoy, whether by myself or with my friends.