In a couple of weeks I'll be starting a regular game at a local brewery. I plan to run B/X using B/XE at the table. I want as few house rules as possible. One rule is regarding thief skills... because as written, they really do suck the big one.
This is just a refinement of an idea I've ranted about for years. I believe this is a very simple way to handle thief skills and goes a long way toward correcting the (IMHO) poorly-designed thief skill set without changing the stats or adding too many fiddly bits.
-Thieves roll their skill on percentile dice + an ability check at the same time. If the percentile roll is good, ignore everything else because they have perfectly executed their subtle craft and cannot fail. Otherwise, go with a simple ability check.
-Non-thieves do sneaky stuff on an ability check, usually with Disadvantage. They cannot do super-secret stuff like climbing sheer surfaces or disarming complex traps (unless the player has a terrific plan).
The idea here is to say that thief skills are special. The thief isn't merely trying to be very quiet or trying to find footholds on a wall. They have been trained or have discovered lost secrets or have tapped into natural talents that normal people cannot access. The thief doesn't simply "hide" in shadows, they fucking disappear. If that percentile roll is a good one, the thief cannot be detected. They are as good as invisible, though not in a magical way.
Failing the percentile roll means they have not executed their subtle craft perfectly and they can be detected or they can fall to their doom. At that point, an ability check tells the story. But note that while non-thieves make their sneaky ability checks at Disadvantage most of the time, thieves do not.
And that's pretty much it. I think this method is intuitive when you describe the thief skills as being esoteric and carefully developed. It has logical consistency and definitely helps mitigate those god awful 10% skill rolls.