I'll chime in a little. Caveat, I've never been a great PK'er, but I did have some relative success with a few characters. Uhgtohg, Odrallag, and Zaahir are probably the three most successful PK characters I've had (all sword spec RBW if you're keeping track) I'd also consider Ahmahrohtar a PK success despite the numbers.

For a long time, I had the same problem you appear to be having. I'd have these great roles, and I'd build a character thinking, I'd covered all the necessary elements, and then I'd get my ass kicked, alot. I can con-die a character with the best of them. In fact probably better than anyone but Shamanman, but I digress.

What changed it for me is the realization that in order to PK more effectively, I had to actually consider the mechanics when I played. Because you mentioned it, let's talk mitigating damage, as an example.

Things that have to be considered (not in any order):
Race
Vulnerabilities
Weapon (or spell) damage-type
Weapon material
Your skill in their weapon
Your defensive skills
Your defensive preps
Their offensive preps
Their damroll
Your ac
Their spells and skills
Your saves

There are others too. My point here is, you have to start thinking with all of these variables from a mechanics standpoint, and that's just to address how much damage they are doing to you. We haven't even begun to talk about your offense, terrain, lag, maledictions, tactics, etc. It's a ridiculously complicated mess.

I had to start thinking about little things like how many characters of each command is the minimum that needs to be entered to trigger it. Lots of people memorize paths from when place to another, but I started thinking about those paths as attack or escape routes.

It's a mindset shift you have to make in how you play, and it can't be as shallow as, that's supposed to be a good build, or I should win that because x is better than y.

Honestly, it sucks a certain amount of fun out of things for me personally. Most of that lost fun is replaced by winning more fights, some of them in rather epic fashion, but the enjoyment I got from the immersion aspect went down. I'm sure it's different for everyone.

Anyways, my two cents, as I did get myself from a really ####ty PK-er to a squarely middle of the road PK-er, and that was more or less how. Good luck.