Casting spells should not train the skill of the spell if they do not accomplish anything. Examples include: casting healing at yourself when you already are at full HP, casting wizard lock in a direction where the beam doesn’t lock anything, or casting an attack spell that fails to hit any monsters.
Skills that you have enhanced in the past, but haven’t used for a long time, slowly lose their training points and, eventually, revert back to lower skill levels and require you to practice the skill again before you can re-enhance it, similar to how amnesia works.
Archeologists should be able to do experimental archaeology with any artifact weapon to unrestrict its skill. Effectively, this would allow them to train the skill up from restricted to unskilled, which takes as long as going from unskilled to basic does.
Skills automatically enhance themselves when you have trained them sufficiently. Also, the skill slot system is removed so that you don’t have to worry about training a skill you won’t want later and wasting its slot.
Your skill practice points gradually decrease with time on their own. They will decrease slowly enough that if you are using a weapon infrequently but regularly, you won’t notice anything, but if you go many thousands of turns without using a skill, you may need to retrain and bring it back up to speed. There should either be a message when your skill falls a level due to this decrease, or when you try to start using the skill again only to discover that your skill has decreased.
Minimize the impact of enhancing a skill. Effects that changed with the threshold should be migrated to scale directly with practice as much as possible. If you have maxed a skill to its next enhancement threshold but haven’t or can’t enhance further, further practice is not counted.
Amnesia makes you forget spells and lose skill points instead of forgetting discoveries and maps. Normally, spell recall is drained; if a spell is at 0%, it is completely forgotten.
Armor of training: has no AC, but gives you a small multiplier to your experience point gains (and possibly skill point gains) whenever you are wearing it.
This could also exist as an object property rather than a new object.
Potion of training: gives you a temporary multiplier to your experience point gains (lasts for the next N monsters, not the next N turns). Might also give you a temporary multiplier to skill training point gains.
Add some mechanic that allows you to pay for training to unrestrict a skill and bring it to Basic. Players of any role are also able to get riding training.
Rather than making weapons train 1-to-1 on all successful hits, make them train differently:
You have access to the full total allotment of skill points from the beginning of the game (effectively making it so that gaining more levels isn’t required to unlock skill slots). To compensate, you can only train skills by fighting at-difficulty monsters or higher, so you can’t train everything by farming weak monsters.
Unicorn horn skill should also be trained by curing things with it, and its chance of fixing something increases with skill level.
Skills should be trained even when damage output is 1 (but cutoffs would probably need an increase). Skill level cutoffs should probably be rebalanced anyway; for example, it should take longer to train long swords than it does for broadswords, and this could add an extra dimension to weapon choice.
Most artifacts should have a negative to-hit bonus, so you’re encouraged to train the weapon’s skill with some weapon that isn’t the artifact.
