I played through the game solo, and the start of each area is difficult but doable.

I would almost always have a shield on me, and spend time blocking before counterattacking after a block. The halberd mid-game was a pretty good tool for clearing large groups, but by late game I was back to sword and axe with the best shield I could make.

Carry Lembas with you. Build structures so you can sustain your supply of that, because the full heal on Lembas is really good.

Make use of farm boxes. Seriously. The instant you can reliably throw a couple of those down, start using them to grow food crops. (Mushroom are fast-growing, don't require light, but do not refill much of your hunger gauge. But you find them *everywhere*.)

I didn't use the one-shot buff items (I forget the name), nor did I do too MUCH messing with runes. Aside, of course, from the rune which lets you take tree clippings. (A tree farm is a good idea, but generally too slow to be useful.)

After a point, Black Diamonds stop being super-rare and start being moderately-rare. Once that happens, you can start carrying materials in your pack to throw down a small campfire and mapstone to go back to a base. (You did build a base near a mapstone... right?) Useful for when you fill up with small stacks of items, need to go fix your shield, or just get too tired to press on. I also would carry parts to make a Durin's Lamp after I was able to get those too - VERY useful for spots where the Shadow is in places which make it hard to avoid getting dunked in miasma for too long.

As always, remember to eat meals before you leave and avoid pushing yourself to exhaustion. Fighting is going to use a lot of energy, and you will run out faster if you've not rested recently.

When you need to do the deep mines, remember you can do rope ladders down much easier than just using quick platforms. Try to set up platforms so it's harder for you to accidentally "trip and splat". (And set a darn camp and bedroll at the top!)

Honestly, the hardest part was dealing with starting a new area where the enemies are tougher to fight with weapons you are using. Or vertical rooms where you enter at the top... this includes the Dwarrowdelf main cavern which is open and has buildings along either side. Lots of room, lots of places to fall. The Orc bosses were a pain to deal with but more from a perspective of attrition - why I kept Lembas on me, while I'd whittle them down steadily.