We say "let's do [SPECIFIC ACTIVITY] at [SPECIFIC DATE AND TIME]." Vague = low commitment.

I disagree with the above poster, though. For me "let's hang out sometime" translates into "Preliminarily, I find you reasonably interesting, but not enough to immediately make plans." The ball is then in your court to propose a specific get-together that is inexpensive and of short duration (otherwise there is too much perceived pressure.) General rule of thumb, if you ask twice and the person says no without a counterproposal of a specific activity, date, and time, they're just not that into you.

This is very American, btw. Neurotypical non-Americans often find this process just as baffling.