The overworld is entirely hand crafted. Note however: The enemies in those areas are grouped into a pool, from which a set of enemies is randomly generated when you walk around in the area. Also, there are random elements and events (or little side-quests) that can appear in the overworld.
Dungeons are randomly generated. Aside from hallways and connecting walkways, which seem to be completely randomly generated, there are certain important aspects of a dungeon which remain the same (such as the part in Act 1 where you recruit your first follower), but even those are still arranged randomly throughout the dungeon.
Books are always bound to certain potential locations. Some are bound to random dungeon locations so whether you will find some of them is random because it is determined by whether those randomly available locations are generated for you. Also, how many books are present to be picked up in a particular area is also random so if there are more books available for an area than the game generates places to pick them up, it is likely that you may not find all of them. I had to visit Old Tristram/Road 3 or 4 times to get all the books there (picking up 1 or 2 at a time).
Certain sets of books are bound to the same location and groupings of them are always found in a set order (I, II, III, etc.) so the books to do with Old Tristram (Cain's Old Journal, Gillian's Diary, Despina's Journal, Lost Journal, Old DIary) can all be found in Old Tristram or on Old Tristram road and you will always find Gillian's Diary Part 1 before you find Part 2.
Certain book parts will only be available during certain acts (Leah's Journal, Deckard Cain's Journal). The only suggestion I have for this until a complete list is posted for the affected book parts is to check back during each quest in the main story.
If you're missing books for a location after exploring the entire area, the only way to find them is to generate a new map instance for the area (Exit to character select and the Resume) after which you will have to re-explore the area. The trick is figuring out which location holds the book that you are missing.
Best Answer
You have to Leave Game in the pause menu in order to get new areas generated once you've visited them.
I'm not sure whether the levels are generated when you reach them or when you start the Act/game/area, but it doesn't really matter - either way the only way to get new levels generated is to leave that game.