I've been avidly following the game summaries of Castle Whiterock.
They're entertaining, but they are also good rules reminders for me.
Perception to spot incoming missiles
I don't always remember this - I just call for a defense roll. But honestly, even a totally alert combatant moving cautiously down a hallway shouldn't get a full, unpenalized Dodge or Block against, say, a crossbow bolt that hums out of the darkness ahead. A PER roll to spot it is fair, rules-appropriate, and makes being point less of a trivial series of "I block it on a 19 or less!" rolls.
Limits of Light
This I do remember, but I don't always remember to enforce penalties on the fringes. So often combat happens within 3-4 yards of the light sources. Often people have Dark Vision spells up or have some levels of Night Vision. But when they don't, I can forget, and call out penalties that ignore the darkness penalties for being on the fringes. They mostly don't apply, but then I don't reward those that find a way not to have them apply.
I need to be better about enforcing those. They are harsh on some PCs, but reward high PER and dark-seeing advantages, making them more worth the points put in them.