Watching French films with english subtitles I have noticed, thanks to a bit more knowledge of French, that I can pick up some of the bits that aren't being translated in the subtitles. I guess that you should watch the film the first time with subtitles on to get the gist of the story, than watch it again without subtitles and try to follow the language. 

Now I am learning Chinese I try to pick out words or expressions I know in the dialogue while still relying on subtitles for the meaning of the story. English subtitles on Chinese films can be an adventure in themselves, if they were done locally and not by SBS. One day I may have enough Chinese to be able to pick what is not being translated.

Whenever this discussion comes up in class, I remind my students that I rarely have this luxury when I watch Slovak TV or films - any subtitles are usually in Czech (if it's a foreign film), and English subtitles are very scarce. The fact is, I simply have to go without any support, watch the footage and try to catch what I can. At least I pay more attention this way.

It's also worth keeping in mind that if you have subtitles, it's very tempting to just focus on them if the film is anything longer than a few minutes. It's probably counterproductive if you have a 90-plus minute movie, because if you really want to understand what is being said, you should watch the film several times. The reality is, despite your best intentions, your attention is drifting towards the sentences written at the bottom of the screen.

I think if you're fairly new to the language, then you should focus on understanding small extracts properly instead of trying to watch a full movie.

For me it was better to read something in French and then listen to the same thing in French.  That helped me to understand spoken French. Movies and music were too indistinct and too distracting.