The Early 24th Century reading list is centered around several series, all of which could be put under the umbrella title of 'The Lost Era" but were not all marketed under that series. The Lost Era is the time frame from the disappearance of James Kirk to the launch of the Enterprise-D. There were the original six The Lost Era novels, and four other novels which referenced 'The Lost Era' brand. There is also the Stargazer series, which takes place in this era, and several other TOS and TNG stories which take place in this time frame. Characters from TOS, TNG, DS9, VOY, and NF are featured throughout.
In addition to the references noted below, several additional novels, short stories, young adult novels, and comics are connected due to various references in other books, or to other books. Two novels are connected by the crossover series Double Helix (which ties into New Frontier.) Thirteen short stories or novellas are connected, two from Enterprise Logs (which references several Lit-verse novels), two from Tales From the Captain's Table (which ties into eight Lit-verse series), one from The Lives of Dax (which ties into the DS9 Relaunch), and one from Seven Deadly Sins (which also ties into three Lit-verse series.)
Dark blue denotes the primary narratives. Read these for the bare bones story. Light blue denotes the expanded storyline. Read any or all of these to go a bit deeper. White denotes every other connected story from the entire Lit-verse, regardless of continuity. Hover for notes.