It depends exactly on how you're dying, but there are few general ways to help keep yourself afloat. Iron Will and its improved variant can help patch up your weaker will save, and Toughness gives you a bigger HP buffer. A feat like Diehard can help stop you from dying, and while I don't consider it an amazing feat, it can help ease the burden if you're very worried about dying off.
Improved Initiative is a great feat that'll help with both offense and defense, as it can better allow you to set yourself up before the enemy can act. Any traits to further increase your initiative, like Reactionary, can be a great benefit as well.
This list isn't thorough at all, but I hope it helps at least a little!
For discoveries to not die there's the spontaneous healing and healing touch, giving you extra HP because you recover in combat.
Using mutagen to give you more AC.
Oh! I forgot to mention. The Second Chance trait is also very damned good in order to keep you alive through the most terrible of saving throws.
mummification also seems good. It gives useful immunities to cold, paralysis, sleep, and nonlethal damage.
Those seem like things that can knock you out fairly well, given the chance.
What is your strategy for fighting right now?
Tumor Familiar with the Protector archetype. This adds 50% to your HP through the built-in shield other (with fast healing 5), and also gives an AC boost through the bodyguard feat.
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Be very careful with the Die Hard feat, since it is, IMO, a really, really good way to get to dead reliably.
If you are still standing with negative hit points, you remain a viable target for an enemy to attack. And it doesn't take much to go from -1 (or lower) to negative Con in a single hit.
If half-orc, you get Ferocity, which is equivalent to Die Hard, too.