Best I can figure, there are two possible timelines to follow for the movies. Both start out with the same two films but diverge from there.

Timeline A

1. X-Men: First Class (2011)
2. X-Men: Days of Future Past (2014) (the Sentinels are created)
3. X-Men Origins: Wolverine (2009)
4. X-Men (2000)
5. X2: X-Men United (2003)
6. X-Men: The Last Stand (2006)
7. The Wolverine
8. X-Men: Days of Future Past (2014) (Wolverine is sent back to stop the Sentinels from being created)

Timeline B

1. X-Men: First Class (2011)
2. X-Men: Days of Future Past (2014) (the Sentinels are NOT created)
3. X-Men: Apocalypse (2016)
4. X-Men: Dark Phoenix (2019)
5. Deadpool
6. Deadpool 2
7. X-Men: Days of Future Past (2014) (Wolverine wakes up in 2023 and everyone is alive because the Sentinels weren’t created)
8. Logan (2017)