THE FIRST AVENGER: CAPTAIN AMERICA
We know its in WW2, so that's that.
IRON MAN
IRON MAN 2
THE INCREDIBLE HULK
In the intro to this film, it shows the origin of the Hulk, which would take place after Captain America, and before Iron Man's origin. But it is tricky, because Stark stopped selling weapons in the first Iron Man, so it is a possibility that the entire Incredible Hulk film, except the end with Banner, Ross, and Stark, takes place before Iron Man.
THOR
Thor is a tricky one. Marvel said that it would be in modern times as well. BUT, if Captain America is indeed the first Avenger, I doubt that it could be before Captain America and Thor would have been alongside Captain America fighting the Nazis. It could indeed be after Captain America, and before Hulk & Iron Man's origin, and they may say that Thor only battles with threats against himself & World threats. And with the historic events that I know will take place in Thor's film, It would be referenced more in the other films.
THE AVENGERS
Then there is the Avengers that'll answer everything. There would have to be world domination.
And the other solo films like, Ant-Man, could be based of The Avengers, like maybe they could cast Ant-Man now, and have him in The Avengers as a normal guy working for SHIELD or Stark Industries.
Then in his film, have his daily job be working for SHIELD or Stark Industries. Then he could be experimenting, and you could guess the rest.