For Star Wars, the storyline is now split into Legends (pre-Disney acquisition) and the new canon Disney Star Wars storyline.
For the Legends storyline, I loved the X-Wings series of books (basically how the Rebels defeated the major parts of the Empire): https://www.amazon.com/dp/B01BJST00W . My favorite book in the series is The Bacta War, there's a lot of small ship action instead of the movies where huge fleets are the norm.
Also in Legends, try the Thrawn trilogy starting with Heir To The Empire https://www.amazon.com/dp/B004WBXM80/ . It's a good set of books with a real threat to the Rebellion.
As for Disney canon, frankly a lot of the books are very meh at best - many of them are just to set up Disney World/Land Black Spire Outpost land. The only one I would recommend is perhaps the new Thrawn trilogy: https://www.amazon.com/dp/1101967021/ - be warned that the second book in the trilogy (Thrawn: Alliances) gets rather slow at times, but the third book (Thrawn: Treason) is actually pretty fun.
