Welcome to the best place on the net, Mia! Hope you like it here and stay for a while. Your question is both complex and simple, and the answer is "It depends!"
1. Sniff a lot! Jot down your thoughts, compare them with the reviews here and on MUA, voice your opinions and retest your fragrances again. I am afraid that my Essentials will not suit you or somebody else, so you have to figure it out for yourself.
2. You can go in depth with either a particular house (say, Guerlain, Caron, Dior, Lutens) or test several fragrances from different houses concentrating on the note/multiple notes that appeal to you (like, gardenia scents, or spicy orientals, or everything with tonka bean, etc). There are fantastic resourses out there with osMoz being just one of them -- with olfactory groups subdivided into families, pyramids, pictures, articles. Check the best of Basenotes -- we are voting each year and nominate best fragrances in different categories -- it should be available from Basenotes home page.
3. Read our threads -- perhaps, you can find your fragrance buddy whose tastes are somewhat similar to yours and you can further explore the wonderful realm of smellies together. We often get a sample, sniff it, form an opinion, retest it and send it on for our other people to try. Or, some samples stay -- we want to sniff it later, or we know that we will never muster up enough courage to wear it on public but would like to sniff it out of the vial once in a blue moon.
4. Browse through beauty magazines to get the scoop of the trends (always with a grain of salt though!) or what is new and coming soon.
5. There is the whole world of fragrances not being advertized in beauty magazines. Depending on where you live and travel, try to get to the closest Needless Markup store to see it with your own eyes. There are blogs where people describe their feelings, and Now Smell This would be a good starting point. There are links to other blogs there on the left hand side.
6. To help you better inderstand what notes are used in perfumery, please refer to our discussions taking place every first Saturday of a month, they are called "Sniff and Speak" days where we all wear scents with a particular note. This coming S'n'S is October 6, and it will be all about amber.
Does this all help any so far?
7. Almost forgot -- budget! It is so very easy to max up your credit card(s) with so many enablers here.
8. Be nice -- read as "responsible in swaps" -- they taught you all about it in the kindergarten!