>The trailer for Infinity War opens with the Guardians of the Galaxy, as we last left them, flying through space on the Milano. Mantis says, "We are arriving," and Star-Lord responds that they need to "put on our mean faces."
>It's unclear what drew them to this location -- whether a signal or otherwise -- but, as they're flying through the wreckage in space at this location, a body bumps into the ship's windshield. They bring the body into the ship and... it's Thor!
>Considering Thor's reaction to the Guardians upon waking up is, "Who the hell are you guys?" it's clear that this is the first meeting between the Avengers and the Guardians. It could be that the end of Thor: Ragnarok sets up whatever causes Thor to be stranded in outer space.
>Notably absent from the trailer is any sign of Hulk, despite Mark Ruffalo being on stage with the rest of the cast prior to the trailer being shown. It's likely that something occurs in Thor: Ragnarok that, if he was shown in this trailer, might be a spoiler for the latest Thor film.
>The rest of the trailer showed the Guardians actively working with the Avengers, and the bulk of the latter half of the footage showed them fighting Thanos directly. One showdown that involved Doctor Strange, Iron Man, Star-Lord and others had them fighting against Thanos on what looked like a wrecked Asgard, or some other planet among the realms. At the end of the footage, Thanos curls his fist, causes a planet behind them to explode, and then hurls the destroyed pieces down through the atmosphere at those he's fighting.
(It is noted that Thanos does this while having an incomplete gauntlet.)
http://m.ign.com/articles/2017/07/15/avengers-infinity-war-trailer-reveals-how-the-guardians-of-the-galaxy-meet-the-avengers