Brandish

The game can be a little disorienting, but just think of the shifting camera as tank controls. There's a button you can hold to "strafe" as well that makes maneuvering around enemies pretty easy.
Most weapons consume durability, but fighting barehanded doesn't, and is pretty effective in the early game. You can honestly just hold out for weapons that don't consume durability to no ill effect, while selling off the breakable ones. Once you get a little more inventory space, it's a good idea to at least hold on to 1 or 2 of the strongest swords you've found for when you encounter tougher enemies.
You can't ever put yourself in an unwinnable state (aside from saving during combat), so if you think you've managed to lose a key or something, try backtracking. Also, check chests, even open ones, because some players accidentally put items back inside after opening them.
Speaking of keys, the first floor has a bag of keys, and behind it, a hole. Usually, falling into this hole just takes you back to the beginning of the floor, but if you jump into it and hold forward, you can access an easter egg zone that contains Warp Magic, which lets you warp to any tile you've been to. It's pretty convenient and makes the game a lot more playable. However, the magic also lets you travel to any tile ADJACENT to any tile you've already been to, which can break certain navigation puzzles. It's up to you how to play, but I would recommend trying to only use Warp Magic for convenience.
Make sure to make use of the Rest function to quickly regain health and magic. If you're in a difficult situation, you can usually cheese your way out of it by closing doors behind you and resting for a bit before re-engaging.
All keys you find are usable on the floor you found them, but some repeat throughout a given segment of the game, so, depending on the reward for using a key, you might want to hang on to it to make later sections a little easier. Definitely drop keys as you transition zones, as they're useless in subsequent areas.
When you first get an inventory expansion (third floor of the Ruins), you also get the ability to organize your inventory and stack items like rings and potions up to 99 to conserve space. This is mostly useful for hanging on to potions and rings. Be careful not to stack potions and poisons together, as you'll lose a number of potions equal to the poisons you mix in.
You might hear advice to hang on to your gold bars and sell them once you've reached a full stack, but this advice is overblown. Stacking gold bars increases their sell price, but only by 0.5%, so it's an increase from 99000 gold to 99450. If anything, just make sure you sell gold bars in even-numbered stacks, and you'll get the same value as saving up.