Ron's behavior for most of The Goblet of Fire isn't his best - jealous of Harry being the center of attention yet again, and refusing to believe that he didn't put his name in the goblet, Ron sulks and refuses to speak to Harry for a large part of the book. Despite this, he manages to make things up with his friend, and make some better decisions along the way - and a teenager can be forgiven for not being perfectly mature!
Still, Ron's sulks mean that he isn't as much a part of this book as he is most of the others in the Harry Potter series - especially as Harry's final showdown against Voldemort in this installment is one of the only ones that doesn't involve Hermione and Ron! Despite all this, though, some of his decisions have a major impact on this year at Hogwarts.
Telling Harry Hagrid Is Looking For Him
This isn't a moment from the books (where Hagrid approaches Harry directly to ask him to meet), but in the movie, Ron es a convoluted message to Harry to let him know to go see Hagrid. While this is certainly not the simplest way for Ron to let his friend know that he will be going up against dragons in the first task, it's well-intentioned - and it does work, which is the important thing!
Thanks to Ron and his choice here, Harry is able to get some forewarning that the first task will be dragons, and come up with a way to deal with that. It may seem like an obvious choice, too - who would want to put their best friend at risk of being killed? - Ron's jealousy and sulking can cause him to make some truly terrible decisions later on (like abandoning the hunt for Horcruxes), so it's impressive that he makes the right choice here, when he is much younger.
Apologizing To Harry
Despite the fact that Ron can definitely show his age and immaturity, especially at this point in the series, he makes the right choice in finally making it up with Harry after the first task. This is noted as a choice Ron makes because he sees how dangerous the tournament in, and realizes that Harry would not have voluntarily signed up - but whatever his reasoning, it's just nice to see him bite the bullet and actually decide to apologize to Harry.
The friendship between Ron and Harry is a vitally important one in the series, and had he not chosen to make it up at this point, it could have caused enough of a schism to change everything. Ron may sometimes seem like a bit of a sidekick, but he's someone who saves Harry's life - so without him, and without this apology, Voldemort may well have won the day.
Asking Hermione To The Yule Ball (Badly)
While the way that Ron asks Hermione to the Yule Ball is absolutely terrible, the fact that Ron asks her at all is still a good choice of his. ittedly, it's not one that is immediately followed by the realization that he cares for her as more than a friend (which takes him years to really figure out), but it is one that starts to pave the way for their future relationship.
This is also a choice that really makes Ron see that not only is Hermione a young woman, but that other people are seeing her as a romantic interest. Ron is, obviously, something of a jealous person - and this rejection may have been the spark to start his romantic interest in his future wife.
Refusing To Tell On Fred & George
In the books, Fred and George's attempts to find the money to open a joke shop are a much bigger part of the Goblet of Fire - but this is played down in the movie, where this scene doesn't make it in. However, in the novel, the Golden Trio find out that Fred and George are seemingly threatening someone for money - and Hermione wants to go to Percy and tell on the twins!
However, Ron is the one who makes the very wise decision not to - and to discourage Hermione from doing so, as well. In subsequent years, it's made very clear that Percy doesn't quite have his priorities straight at this point, especially with family loyalty, and that Fred and George were in the right in this instance, so it's definitely a good thing that Ron stopped Hermione from telling on them!
Helping Harry Study For The Last Task
Again, this is a scene that doesn't make it from the page to the screen, but in the books, quite a bit of time is spent on Ron and Hermione helping Harry to study for the final task. They spend hours and hours looking through books, learning useful spells, and practicing defensive magic - all of which would come in extremely handy for the Golden Trio later on!
Ron's decision to help Harry in this way was a good one for so many reasons - not only did he help Harry learn the skills that would end up saving his life later on, but he ended up learning quite a few of them himself! This also showed his loyalty to Harry, and managed to completely heal the rift between them from earlier in the year.
