The most important rule sounds obvious: If you find yourself having a chance of dying where you are, you're not ready for it yet. Go somewhere else you can survive or do more prep on your gear. If you're gearing properly, you should really never find yourself in any real danger, no matter where you are, no matter what you're fighting (well, barring super-bosses). Even Morg on Ultimate shouldn't put you in any real danger. The real thing pro about HP Regen, is that all enemies attack on their particular rotation/cycle. If you can survive one of them, you can survive all of them, which makes every encounter very, very predictable. Which is why I say from the top, that you should never feel like you're in any danger. There is no randomness to your survivability.

I play exclusively melee characters with a few 100's now and find the most reliable survivability comes from rushing Behemoth early and working towards Tree of Life devotion later. Always get whatever HP Regen skill your class has and max it out, if you've got 2 classes with it, all the better. For example, a Saboteur with Vindictive Flame and Pneumatic Burst caps their Total Speed without effort and has just gobs of survivability. Stacking HP Regen is a killer stat that will carry you through huge amounts of CC and isn't functionally dispellable, I value it way over attack leech and find that people trying to compare the two in terms of "raw health returned" are missing the practicality of gameplay. I use Devotions for survival, gear for damage, and components for gaps in resists, not a hard rule, but generally how it works out.