Clearly many movies have traditional three act narratives but, these days, with lots of subplots and tie-ins. I chose what I thought would be a simple rom-com - Crazy Stupid Love - to illustrate this point and actually found it to be quite complex with there being several elements at play all at once. It is useful to analyse this by identifying the emotions involved in order to spot the key moments of drama.
Often films have the scene-setting stage, followed by ascending action, some sort of climax or confrontation or disaster and then a resolution and conclusion. There will be incidents along the way to trigger various plot elements and usually the characters go through some sort of transformation.
There are great diagrams on the internet to show how narratives can be mapped out - often in the forms of graphs or flow charts. I found it easier to try something that looked more like a mind map but this encourages the inclusion of too much detail really.
This is a superb diagram of this type of structure:
I've found that when I am trying to come up with narrative ideas, this is all fairly instinctive as we have got used to it in books, films and plays. It is still a good idea to test this though as otherwise the work may fall flat.