1. Rogue One: A Star Wars Story
Whichever way you watch the Star Wars movies, Rogue One recaps that first paragraph of the opening crawl of A New Hope. Unless you're doing release order, or you absolutely want to start where it all began, Rogue One belongs before A New Hope in a watch-through. Treat it as a prologue to the saga.
2. Star Wars: Episode IV - A New Hope
Where it all began. The first paragraph of the opening crawl recounts the events of Rogue One; arguably this makes Rogue One skippable, but it's a brilliant movie worth watching. From here on out, it's the main saga, the Skywalker family and their friends.
3. Solo: A Star Wars Story
Flashback! I've debated where Solo fits in a watch-through, but I think it makes most sense between A New Hope and The Empire Strikes Back. Han Solo's main character arc concludes in A New Hope, and from here on out he's an established hero. His character and history is pretty central to Empire, though, so it's worth visiting this movie here. Without it, details of Han's history with Lando Calrissian are rather sketchy, but the film is otherwise entirely skippable.
4. Star Wars: Episode V - The Empire Strikes Back
The dramatic turn - a victory for the dark side of the Force. Arguably the best Star Wars film of all, with the biggest, most memorable twist that... everybody already knows, regardless of if they've seen Star Wars. Still, this movie establishes an enormous crisis for the heroes, that - at the time of release - wouldn't be resolved for another three years.
5. Star Wars: Episode I - The Phantom Menace
Flashback! Vader has just claimed a victory in Empire, and a dramatic reveal has shook our heroes. It's time to visit how the Empire came to be and how Vader came to be Vader. Along the way, we'll learn about the prophecy of one who will restore balance to the Force.
6. Star Wars: Episode II - Attack of the Clones
Arguably the worst Star Wars movie of them all, but it continues the rise of the Empire and demonstrates how they claimed their might and how the emperor usurped power from the Galactic Republic.
7. Star Wars: Episode III - Revenge of the Sith
Easily my favourite of the prequel trilogy. We see the culmination of Vader's origin, the event that all but ended the Jedi order, and our favourite characters are moved into their starting positions for A New Hope.
8. Star Wars: Episode VI - Return of the Jedi
End of flashback. In the prequels, we have seen the rise of the Empire and the fall of the Jedi order. In The Empire Strikes Back, we've seen dramatic twists and our heroes left on the back foot. This is what it has all been leading towards - a final conflict between the Empire and the Rebel Alliance and a battle to restore balance to the Force.
9. Star Wars: Episode VII - The Force Awakens
Cards on the table: The sequel trilogy are quality movies but... they struggle to find a meaningful place in the Star Wars saga. The Force Awakens is largely a retreading of A New Hope. The Jedi are a legend, the First Order have risen from the husk of the Empire and the Resistance fights to protect the New Republic from their increasing might. The story sees new characters - Rey, Finn and Poe - attempting to deliver a message to the Resistance led by General Leia Organa (formerly princess Leia).
10. Star Wars: Episode VIII - The Last Jedi
The Resistance has its darkest hour, as it attempts to flee the relentless First Order to no avail. Luke Skywalker has lost faith in Jedi traditions. It is a time when hope is all but lost for most, but not for General Leia Organa - her faith in the people of the Resistance maintains morale against all odds.
11. Star Wars: Episode IX - The Rise of Skywalker
The prophecy has been cheated! A new Empire looms as the Resistance fight desperately to end their tyranny. General Leia Organa fulfills a promise spoken in The Empire Strikes Back - Obi Wan: "That boy is our last hope."; Yoda: "No, there is another." - but can balance be restored?
I mentioned Leia in every summary of the sequel trilogy, there. Like I said, it's difficult to find where they fit in the saga; their vision is not as clear as in the original trilogy or even the prequels. In general, they are better films than the prequels... but the question of whether or not they belong in the saga is a tough one. My answer to that is this: They are Leia's trilogy. Prior to their release, the prophecy of one who would restore balance to the Force was assumed fulfilled by the end of Return of the Jedi. These films seem to undo that, and I argue the case that a certain character has cheated the prophecy - they knew about it, planned for it, and cheated their fate. But when you mess with fate, fate tends to mess back. Where once Luke confronted Vader and brought balance to the Force, the secondary disruption is rebalanced through Leia's relationships with important characters - she trains a Jedi apprentice, she reaches out to a conflicted Sith, she inspires hope and optimism in the forces of the Resistance.
If the original trilogy is Luke's trilogy, I argue, and the prequel trilogy is Vader's, then the sequel trilogy is a prophecy cheated and is Leia's trilogy - through her, and through two lineages each arguably matching the prophecy, a dyad in the Force is created that undoes the cheating of fate and restores balance to the Force once again.
It's a... strained and inconsistently told chapter in the saga, but I believe this interpretation works. The prequels and sequels have always been kind of difficult to love, but there is some wonderful stuff in them that makes them at least worth considering.