Stuff in Black is from the trailers, stuff in purple is speculation
Knowhere
Gamora explains the plans of Thanos to ???(perhaps the guardians)
Flashback scene shows Thanos collecting a young Gamora
The Guardians head to some place dangerous on the Milano
The Guardians are on a planet doing ??? (maybe trying to take the reality stone from the Collector for safekeeping)
The Guardians come across Thanos or one of the Black Order questioning The Collector about the reality stone
The Collector says that he has sold it
Drax attacks whoever is questioning The Collector, but survives the encounter
Asguardian escape ship
Thanos captures Thor and Loki after the end of Ragnarok, and kills off a ton of Asgardians. Banner escapes on the Quinjet.
Thanos tortures Thor while the The Black Order holds Loki
Loki offers the tesseract to Thanos
This is probably an effort to save Thor. Thanos may kill Loki immediately, while abandoning Thor on his ship. This is Kevin Feige saying something "really bad" will happen in the first five minutes of Infinity War.
Thanos crushes the Tesseract
Thanos places the space stone in the infinity gauntlet
Thanos then heads to Xandar.
This is when the Guardians probably come across Thor, while tracking down the space stone.
Thanos presumably destroys the entire ship. Thor gets thrown out into space, and lands on the Milano.
The Guardians take Thor into the Milano
Thor meets the Guardians
New York
Banner crashes into 177A Bleecker Street
Strange explains the infinity stones to Stark, and what Thanos is out to do
A portal appears over NY
Spiderman's spider sense gets triggered
Spiderman looks at a portal opening up over NYC
Spiderman leaps out of a school bus to investigate the portal
Wong, Strange, Banner and Thor look at at a disturbance outside Bleecker Street
Stark goes to see why people are running helter skelter
Strange, Banner, Stark and Wong look at same portal
Iron Man flies towards a spaceship on Earth using the new Bleeding Edge suit
Strange activates the Eye of Agammoto
This is the "portal ship" that probably takes Strange, Spiderman and Iron Man to the orange planet. Banner heads out to warn Vision and save the Mind stone.
Banner, Widow and War Machine look up ??? Quinjet to take them to Wakanda
Xandar
Thanos destroys a bunch of Nova Corps ships, and collects the power stone.
Peter meets Strange
Thanos arrives on Xandar
Star Lord, Stark, Drax and Spoderman make plans
Spiderman jumps through destruction
Strange and Star Lord fight together
Thanos jumps towards ??? (maybe spiderman)
Thanos Pins Spiderman to the ground
Thanos already has the power stone and the space stone when taking on Stark
Thanos tells Iron Man "I hope they remember you"
Thanos lobs a freaking moon at the Avengers
Maw tortures Strange
Wakanda
Banner, War Machine, Vision, Witch, Widow and Cap all end in Wakanda to safeguard the Mind stone
Black Panther welcomes Team Cap to Wakanda
Shuri looks at a hologram of Vision
Black Panther orders to put up the defences of Wakanda, as well as a shield for Cap
Wakanda is the most heavily guarded place on planet Earth, which is why Vision is being kept there
Wakanda
Vision appears in human form, maybe Witch is giving him a vision
Vision says "we are out of time"
War in Wakanda, with the outriders taking on Team Cap
White Wolf fights with Team Cap
Banner and Widow smile on the Wakandan battlefield
Thanos goes toe to toe or hand to hand with Cap, wearing the power stone and the infinity stone on his gauntlet
Massive alien ships land on Wakanda
Proxima midnight lobs her spear at ???(maybe Cap), who catches it
Witch is relieved by something, in the same scene as (?Cap) and Proxima Midnight
Black Widow stabs someone, probably in the same scene as (?Cap), Proxima Midnight and Witch
Corvus Glaive attempts to take the Mind stone from Vision. It is unknown if he succeeds.
Nidavellir
Groot, Rocket, and Thor are on a ship with a circular window like the Cupola on board the ISS.
Thor looks over a planet through the Cupola, probably Nidavellir. He needs a new weapon to take on Thanos.
Thor is in some huge device, probably forging a new weapon
Groot and Rocket help Thor forge the Jarnbjorn or Stormbreaker