News values means that some events are seen as more or less important by news producers. Stories have 'value' and their value depends on what the story offers.
Galtung and Ruge- Negative news stories are given more importance than positive ones
proximity matters, were also given more space and importance, eg close story geographically will get more news space in a paper or other form of media,
recency- did it just happen? is it breaking news? the more recent the event the more important it seems,
currency- if a news story or event is ongoing for a long time it may be given more space- eg Brexit's longevity, newspapers may be more willing to report on something that has been going on for a while
Continuity- they know a story will give them lots of stories to follow up with, things to use out of stories
uniqueness- if something is unusual or does not happen often then the paper may want to report on it,
simplicity- easy to understand stories has a higher likelihood of a paper reporting on it, newspapers will often simplify complex news stories
personal/human interest- when a complex or otherwise everyday story can be made to feel more personal by focusing on an individual case.
expectedness- if readers might expect a story to be featured, a newspaper will be more likely to report on it, eg regular events like bad/good weather, GCSE results being released etc
stories featuring 'the elite' eg celebs, are given a lot more prominence in most newspapers.
exclusivity- if a paper has a story before their competitors, they are more likely to cover it,
size- the more people affected by the story/event, the more value it has
these ideas should help you understand why some stories are much bigger or smaller than others, and why some stories might not even getreported on at all.