I look for adventures with elements of horror and mystery. I try to avoid pure dungeon crawls, because a vast bulk of skills tend to go unused in them. The guy whose talents are all in Persuade, Sailing, Survival and Animal Handling will have very little to do in The Tomb of Horrors. Plots involving intrigue, overland travel, a general variety of settings and situations is good. When rewriting them, I focus on bringing the Doom mechanic to a prominent role in the plot. If the old module says “This event happens after X hours have passed,” I change it to “Spend Y Doom to make this event happen.”
Another thing I look out for: most D&D adventures lean on two devices for creating action: traps and combat. A lot of them have way too much combat for a Conan scenario. In my opinion, traps and combat often end up feeling obligatory and monotonous–especially in the classic modules.
Conan gives GMs much more to work with for action scenes. Hazards can be anything that would fit naturally into the environment; they give writers and GMs the chance to make the environment shine out as an antagonist in its own right, rather than “This hallway is randomly trapped with a swinging scythe because it’s time for some dice rolls and damage now.”
So, I look through areas and replace traps with hazards. A random spring-loaded pressure plate becomes an angry scorpion hiding in some rocks, or a sharp draft that extinguishes torches and creeps the PCs out for mental damage. The odd mechanical trap might still make it through, but in my opinion they are used so excessively in D&D that they become quaint.
Combat too often needs an overhaul. This game gives writers a very easy time designing flexible combat scenes, and GMs have plenty of tools to correct scenes that turn out too easy or too tough. So, when I’m rewriting a combat scene, the first thing I do is ask myself if combat even belongs in this part of the story. Like I mentioned before, D&D tends to throw a lot of random fights at players, because it doesn’t have many other tools in its belt. Too much combat in Conan will make the pace suffer. Trust me, I’ve made this mistake. Often, I can just take out a needless fight scene and replace it with an unsettling setpiece or narrative, an event that might generate Doom, a hazard, or an obstacle that isn’t outright dangerous but might require a skill test or two.
Then, I look at the CR relative to the intended party level. A trivial encounter in D&D (CR = APL-4) gets redesigned into 1 Minion per PC, or a single Toughened foe. Slightly tougher but still easy becomes 2 Minions per PC, slightly harder becomes 4 Minions per, or a Squad with a Toughened leader. And so on. I include advice for GMs on ways to use Doom to increase the challenge.
Finally, I find most boss battles need to be revised. A scary monster in a room does not cut it for a Conan boss scene. There need to be environmental hazards, a ticking clock, a damsel to rescue, etc. The more chaotic, the better.