If you unlock Charme, which you should, as she's fast, and fun to play, fighting the tentacle monsters can be risky on low health. Which Charme often has, being a thief...
The safest way to fight them, and for that matter the bouncing mushrooms and wasps which are also a pain, is to face the monster and cast her ghost skill. Then you can happily fight at a distance without risk. If you time the hits right with tentacle monsters, you can kill them in one hit as you'll be hitting them from behind!
I thought it'd be really clever to put the image behind me and walk away from monsters while able to attack them to keep them away; don't try this. I realised after dying that hitting monsters moves them in the direction you're facing, not in the direction from which you damaged them. Which way are you facing while running away? So yeah: don't try to be clever like this.
Never throw away food; always eat it. If you're near a next floor portal and have lots of health, drop the food there so you can eat it just before you drop down. Try to keep some food on your inventory at all times; even walnut bread can safe your life. If you're on half health and only halfway to levelling, eat something. You'll probably need to anyway, so it's best not to wait until it's an emergency. If you're low on food, be really, really cautious: You'll likely need some food to fight Charme on Jade Way if your skills are as bad as mine!
If you're low on health and get hit, immediately pause to evaluate the situation properly. If you'll die in one more hit and think it's possible you will get hit, eat something.