Avengers: Infinity War - Predicting The Entire Plot In 20 Steps

6. Thanos Defeats The Avengers/Guardians Alliance

Despite the number of heroes working together to try and defeat Thanos on Titan, his first proper encounter with the Avengers and Guardians has to end badly for the heroes (partly because they need to see the lesson that it will take ALL of them to defeat him). The fact that the Titan is able to monologue somewhat while he fights them suggests everything about how much of a threat he's under.

From the trailers we know that Spider-Man will be in trouble and that Iron Man's suit will be destroyed (luckily Titan's atmosphere is breathable), while Thanos will drop an entire moon on the heroes to gain victory before he escapes (presumably without the Time Stone). Expect one of his daughters to be killed in this exchange (unfortunately, they're both expendable and impactful as deaths).

By the look of Tony Stark during this sequences in the trailers, he expects this to be his end, but it's unlikely he's going to be killed off here. Maybe wait for Avengers 4 for that...