Books as Character Advancement
A book can provide a character with a skill. For example, +1 to hit with a scythe (see above). The character accesses this benefit after a single evening of reading a particular book and will continue to have that particular skill so long as they are in possession of that book and the book is completely undamaged (characters are assumed to be reading the book during downtime, a player isn’t required to say ‘I’m reading my book’). While characters can only use the skill derived from one book at a time, characters can absorb a book’s skill permanently by studying the entire work. It takes one evenings worth of reading to transition from one book-skill to another.
Studying a book is a lengthy process, the average book takes 3d20 evenings to completely study (add more d20’s depending on how useful and broadly applicable the skill being taught is). This amount of time is only discovered after an evening spent reading the book. Studying is modified by a character’s intelligence; subtract a character’s intelligence modifier to each of the d20’s rolled. The minimum number of evenings to study a book is 7. This amount of time is character dependent and should be rerolled if the book is lent to another player character.
The player is expected to keep track of each evening spent reading, tallying towards the total completion of the books study. An entire day spent reading counts as 2 evenings. While players do not have to announce they are reading, tallying should not be done retroactively - if a player forgets to read (and keep tally of their reading) so did their character. However, once a character has finished reading a book that skill is now permanent and should be recorded as such on the character sheet. Now a new book can start being read and a new, additional skill can be obtained.
Forgetting. Should for whatever reason a player stop or be unable to continue reading a book, not only will they lose (after a single evening) that book's derived skill, they will forget their study progress after an amount of time. To keep things simple and save on daily tracking or juggling dates, a character is assumed to have forgotten their progress (on any and all books they are not currently reading/in possession of) after they have levelled up. A book being read during levelling up retains its study progress whilst others are forgotten.
Learning Languages from Books
Learning a language from a book follows the same rules as learning a skill from a book. While a character is in possession of a language-learning book they can attempt to speak the language detailed in that book. To do so a character rolls under their intelligence score with a d20. The character must make an intelligence roll every time they speak. If the character is successful what they have said is understood clearly. If unsuccessful the character must roll/reroll a reaction roll at -2, whatever was said may cause great offence or inadvertently improve the situation, the DM will tell the player what they actually said. Once a player has completely studied their language-book the character can competently speak that language.
Learning Lore from Books
Players with a high intelligence often ask ‘can I roll to see if my character knows X pertinent detail about Y piece of campaign lore?’. With this book rule you can say yes or no. Lore-books allow players to ask and answer specific questions about a campaign’s lore - or the author’s interpretation of the campaign’s lore. Detailing the author is very important.
Just as with other books, when in possession of a lore-book and having read if for one evening, a player character will be able to ask relevant questions about the book’s subject matter. The DM will attempt to roll under the character’s intelligence score in secret. If successful the DM will tell the player the correct answer, if the roll is unsuccessful the DM will answer with the author’s biased/antiquated/bizarre/misleading answer. When the book is finished being read, the character can be assumed to have a good knowledge of the topic, the player can have their questions answered truthfully without having to roll under their intelligence.
Lore-books are best used for very specific topics, don’t have a book that allows a player to ask questions about all dwarves everywhere, have a book on a specific dwarven stronghold or the common gods of the dwarves.
Learning Spells from Books
Non-magic users can learn spells. A spell book can be read as any other book can be. When a character possesses a spell-book and has read it for a single evening they can cast a spell as a 1st level magic-user/cleric once per day (provided they continue reading the book of an evening). Use your system’s spellcasting rules or have the character roll under their intelligence score when they attempt to cast the spell - if they fail, roll on a spell failure/chaos table of your choice, otherwise the spell is cast successfully. When the book has been studied fully the character can cast that spell that spell without fear of strange eldritch occurrences. Non-caster characters lack the magical aptitude to learn spells above 1st level.
Character finds book.
Character reads book in the evening.
Player rolls 3d20 to see how long book takes to read, subtracting their intelligence modifier for each d20. The roll equals X evenings, minimum 7.
The following morning the character is able to use said book which provides them with a skill/language/spell/knowledge.
Only one book can be read at a time.
After X number of evenings the character has learnt the skill and no longer requires the book to use the skill/language/spell/knowledge.
Character starts reading another book. Repeat.
If character starts reading a different book before finishing the first one, the skill obtained from the first book is lost at the end of the day and the new skill (from the new book) gained the following morning.
Characters lose their reading progress upon levelling up if they are no longer reading a book or if it is lost or damaged.
Just a few example skills and books to be found in your campaign:
Etiquette, +2 to reactions when dealing with certain people/creatures - On the Fey-Courts of the Waxwood Fairies
Survival against X, roll +2 on saving throws against a certain thing, for example ghosts - Beatitudes Against Apparitions
+1 to hit with any specific weapon, the more specific the better. Fighters cannot benefit from books written about common weapons such as swords - The Garotte Codex; how a man shall be slain
+1 when escaping from or initiating a grapple/wrestle. Not a flat +1 to all grappling manoeuvre, something specific - The Pugilistic Deeds of Ordlaff Strong-Arms
+1 bushcraft. If running LotFP, be sparing with skill books. They should be rare and written by masters - The Scrolls of Green Cernunnos.