I recommend starting with the first X-wing book. They are the first Star Wars books I read and I still think they’re the best. It’s a series, but each is a stand alone book so you can take as much or as little as you want. Plus, it really is an island in Star Wars continuity. The series is pretty much self contained so you don’t need to know anything going in or worry about elements from other books appearing and possibly spoiling other stories.
The first four books in the series follow the Rogue Squadron and after that it switches to the Wraith Squadron. None of these books follow the main characters of the movie which I think is their strength they allow the universe to grow to include new heroes rather than pretending Luke and Han are the only ones that save the galaxy every time something goes wrong. Thank god it’s in a galaxy far, far away. Shit’s always going down there.
Whatever you do don’t start with any book that mentions the “Yuuzhan Vong” on the back. Their plot goes on and on and you just don’t want to start there. It’s like being digested by a sarlacc for a thousand years or so.