Okay, I am making much better progress with this game and have been getting to the final fight with some regularity (and keep losing!). What has been working for me so far are the following:
1. Using my abilities frequently. When I see any single enemy in line of sight, I just shoot it with line breath immediately. Breath and Bite recharge fast--like maybe 3 moves?--so you can fire, retreat a bit, and fire again. They don't run out of "ammo" so there is really no need to conserve. Line breath also kills things fast so you don't need to heal as much. I think of it as a sniper rifle.
2. Waiting until after my abilities recharge before exploring. You don't want to get caught without your guns loaded!
3. Not eating until I am at least 33% hurt. Crawl taught me to eat chunks as soon as I can. That is not true in Drakefire. In this game, you want to eat chunks as late as you can--ideally after you've cleared the floor and can choose what stat you want.
4. On named NPC levels, I try to create a pile of corpses in good fighting areas like a corner or corridor. I'd lure a rat or bear or something easy to a good spot like that and kill it but not eat it. Repeat until I have two or three. Then when I run into a named NPC, I retreat and try to lure them to that spot, and from there I blast or bite. NPCs can do mongo damage so having several corpses nearby means I can heal quickly in the middle of a major tussle.
5. I've been having good luck picking up Hardened Scales, MR, and Frightful Presence (in that order). All of those seem to boost my defenses quite a bit, esp against those ranged casters.
6. Pillar dancing works well against the melee NPCs. That is, when I see one, I duck around a set of walls and just move away until my breath or bite attach recharges, and then go in for the kill. It works way better than just standing there and duking it out while you wait for the recharge.
7. Wall hugging is very important when exploring bigger rooms--i.e., I explore a big room by going around the outside, never going into the middle until I see it is clear. It cuts down the number of enemies that can see you at one time.
8. Trample is good against solo named NPCs. Lure them into a corridor and charge. It stuns them and then you can go for the bite! And its range is actually 1 more than what the highlight shows. If the enemy is one step beyond the end of the highlight, they WILL get hit.