As I've mentioned, I've not always been a rules-light player. Far from it. I learned D&D 3.5. I learned GURPS, for Christ's sake. But now I'm old and impatient. I don't get to game as often as I used to, and I don't want to waste precious time on needless dice-rolling, let alone on figuring out the level of your skill level in Abacus Use. (Yes, GURPS had an Abacus Use skill.) So I'm ditching it. It's gone.
Instead, I will be using the following key principles:
1: You are assumed to be a competent adventurer.
Can you climb the wall? Can you ride the horse? Can you swim across the river? Can you sneak up on the guards while they're distracted? Can you spot the clue you need to continue with the adventure?
The answers are yes, yes, yes, yes, and fuck yes. If it's something a brave, capable adult who's grown up in a fairly rough-and-tumble society should be able to do, then you just succeed. No rolls needed.
I don't assume that my PCs are bumbling incompetents. I assume that they're pretty cool, pretty tough, and pretty clever. Anything a bunch of cool, tough, clever people should probably be able to accomplish doesn't even deserve a dice roll.
2: You are assumed to be pretty damn awesome at things related to your class
You know all that cool 'wilderness lore' stuff that scouts and rangers and hunters do in movies all the time? Knowing which berries are poisonous, spotting which way people have gone from broken twigs, finding the one source of water in the middle of the desert? If you're playing a traveller, that guy is you. No rolls needed. You just do it. You're just that good.
Same goes for fighters with tough-guy stuff (of course you can kick the door down), scholars with knowledge stuff (of course you can read the inscriptions), and tricksters with tricksy stuff (of course you can sneak up on the guards). Only really big, impactful stuff even deserves a roll. The rest can just be taken for granted.
3: You are assumed to be able to do the other stuff you should logically be able to do
If it's been established that your character grew up in a fishing village, then you can catch fish, operate fishing boats, and so on. If they were a blacksmith's apprentice, they know basic metalwork. These kinds of 'assumed knowledges' aren't nearly as 'strong' as class abilities - growing up in a fishing village is no guarantee you're any kind of master angler, after all - but they do carry weight.
I am perfectly happy with asking my players things like: 'So, did any of your characters grow up in the mountains?', and incorporating their responses into the scene. That then becomes a new fact about their character. Anyone attempting to string together some nonsensical backstory to justify their possession of a whole range of such background skills will just be politely told to stop.
4: If you attempt something really challenging not covered by your class, roll a dice
The trickster can sneak past those watchful guards. She's just that tricksy! But what about everyone else?
Pick a relevant ability score. If you can roll equal to or under it on 1d20, you succeed. The GM can assign bonuses or penalties as they see fit.
There. That was painless, wasn't it?
5: If you attempt something super-challenging covered by your class, roll a dice
Class abilities have limits. The fighter can kick down the door, but can she bend the bars of the prison window? The trickster can filch a pie from the pie-shop, but can she steal the key to the dungeons from the jailer's belt?
Whenever someone tries something that's within the domain of their class abilities but is also really challenging and impactful, the kind of thing that has the players on the edge of their seats waiting to see if they succeed or fail, then they make an ability score roll, as above. The GM can assign bonuses or penalties if necessary.
* * *
This is all you need. I promise you. If you want more then that's fine, that's great, there are loads of games out there that will give you a million-and-one ways to exactly quantify what your characters can and cannot do. But this is all you need. It gets people away from thinking about numbers on character sheets, and towards thinking about characters as people.
Can your scholar cook? Can she sing? Does she have a passion for flower-arranging? Is she any good at calligraphy?
You tell me.