If it is important to you to be trendy, then it does make sense to research what's the latest thing. I just had a peek at the website you mentioned, and it looks a bit like they are quick snapshots of different fashion ideas. You could certainly do research on trends. The problem with this would be that you might not get much wear out of your dressy clothes, because trends can go by very quickly.
It might help you to find a few stores (online would be the easiest) and look at what you are drawn to -- what colours and styles, keeping in mind what rachylou and BC have said about judging what kind of occasion you need to dress up for. It would also give you an idea of what budget you would be looking at. Again, you might go for something simple that you could wear multiple times, not just once.
Note that it's important to actually try things on in real life and assess whether they suit your body type and personality -- whether they express who you are. You want to feel like yourself even though you are wearing special clothing for your fancy occasion.
I hope this helps? I don't think there's any one answer to the questions you're asking...
