Science Fiction is an attempt to foresee a possible, if improbable, future and tell a story there.
Hard SF is more tightly based on what should/may happen, should progression go along that Path. Mainstream examples include a fair bit of Cyberpunk, 2001, and certain arguments could be made for certain parts of Star Trek, as they could be made that it belongs in Soft SF. You can also argue that Star Trek is just a morality play that got set in the 23rd century so it wouldn't cause an uproar that Uhura's fourth in command of the Enterprise.
Soft SF has taken the license to ignore what physical laws we think govern the universe. Star Wars and other space operas like Firefly go here, but don't take Soft SF to mean that it isn't deadly serious. The Foundation novels can go in here, Dune, any number of other genre-defining novels will also belong here, and it's definitely more of the genre than Hard SF.
Then again, this is all relative and some people will argue that the lines between Hard and Soft can never be fully drawn. Or that it's better that they're not. Maybe we should think of Hard and Soft SF and the border between them like we think of the border between Lichtenstein and Belgium (pardon my French). Sure, it's both real and important, but on the other hand who cares what it looks like exactly? (Well, except to the Belgians and Liechtensteiners.)
Honestly, what's good SF is good SF and what's bad SF is bad SF. Distinctions past that are usually boring and unnecessary.
After that it's just quibbling over if the walls should be Cerulean or Topaz.