Don't try to take on too many enemies at once, keep your pomanders at the ready in case you get screwed over by an invisible trap.

For Bosses, mostly just need to learn their mechanics, which for the most part shouldn't one shot you and you definitely want to make sure you've got an active Pomander of Steel and Strength on you.

Also the Job you're doing it as matters, Warrior is a good choice for surviving most things in Solo Deep Dungeons.