You might also want to check out the Starfleet Academy series that was out in the 90's. The first three books by Peter David feature Worf (plus a number of characters who would play major roles in the New Frontier
series) only 4-8 years before Encounter At Farpoint
(unfortunately Tasha Yar does not appear).
But then there are also the Young Adult Deep Space Nine
novel series that was running at the same time that featured adventures of Jake and Nog on DS9 (with one book featuring Alexander and being part of the Day Of Honor
story arc), but are set, primarily, between the episodes of Seasons 1 and 2.