Damn your live RTDing on days when I must submit to wage-slavery!
Alright, so now I've got some weird system stuff I'm trying to figure out.
I think the basic setup for skills and abilities will work something like as follows:
Skills will be indicated by a numeral to show their rank, ie Farming 3. The experience cost to improve a skill is equal to some variation of the skill level in question, so Farming 1 might cost 10 exp, going from Farming 1 to Farming 2 would cost 20 exp, and so on. Not sure if that'll actually be 10/20/30 or 1/2/3 or what, but something simple and intuitive like that.
Generally speaking, skills add their skill level to the results of an attempt to use them, rather than to the roll. So Swords 2 would add +2 damage to a successful hit, Farming 3 would add 3 Food to harvests, Masonry 1 would add 1 progress to building something, and so on.
Where this gets kind of strange is the way I want experience to work, though. Specifically, while you gain experience by using the skill in question, you have to spend it manually. This has two connotations to it.
The first is that you can spend experience in a related field rather than the one you actually got exp by practicing. So someone who gains 5 Woodcutting exp could potentially use it to level up their Axeman skill instead (incidentally, this is also how magic will work; you progress from something you can actually practice into something you couldn't do normally by chaining skills). I'm unsure if there should be limits on this or not, such as to avoid a master swordsman doing all his training by harvesting wheat.
I do like
Wax On Wax Off skills. You'd want to group skills somehow, such that XP earned Woodcutting could be applied toward Axemanship, but not, say, Fishing. Depending on how many skills you want to futz with, you could have a system where attack/damage/dodge are broken down into smaller sub-skills, with each subskill coming from a variety of skill groups.
You might also have an Attribute system, such that XP for a certain group could be applied to one of your Attributes (you could level your Woodcutting skill, or increase your Strength score, for example.) Thus, you'd have Weapons skills, and Woodcutting skills, and damage would use Weapons+Strength; leveling up, you'd have the choice between improving your productivity or indirectly improving combat ability. Attributes would be more expensive than skills, but would allow indirect improvement of combat ability so you don't have to risk fighting.
The second facet, and the one I kind of need help on, is figuring out what kind of an action spending experience takes. I'd kind of prefer it to be an actual action, in other words, instead of just leveling Farming by farming, you have to take time off your mundane stuff to actually apply that knowledge and make yourself better at it. This kind of raises questions about how exactly that works; should there be a set experience count you can do per turn, so to go from Fishing 3 to Fishing 4 takes, say, one day per 10 exp, or 4 days total? Or should each level take a day, meaning you basically just get the levelup and then take a day off to actually gain it? Or something else, like exp being freely spent, meaning it's more efficient to actually spend your stuff as rarely as possible, or all excess exp disappearing when you level, meaning you want to train as soon as possible once you've got the amount?
I'm not a big fan of sacrificing actions to raise skill, especially if it isn't a super significant increase in productivity/ability. If skilling up was its own action, I'd want to get a benefit besides the skill itself- I got better at farming itself by farming, so if I'm meditating on my farming I should hope I'm getting the ability to summon carrots from nothing or something supernatural/extraordinary like that.
Although actually, now that I've reread that you never said exactly how XP itself is gained- if it isn't tied to the skill at all, then yeah, I can dig it. I would probably argue against having excess XP disappear, since the waste makes me cringe. You could require it to be immediately allocated if you don't want people sitting on piles of XP.