Karly, you raise an interesting question. There is no single simple answer to this question as this is different for everyone. The question states it in that it is "your" perfect career and specific to your wants and desires. For some people it is working with very meager funds in foreign countries to help those less fortunate. For others it is working in large cities making mega bucks. The challenge is figuring out what it is for you.
I recommend finding out what your strengths are by using the book Strengths Finder 2.0. It can be found on Amazon pretty cheap. It provides an on line assessment of your strengths and provides some insight into what each one is good for.
Once you find your strengths, look at your interests. Make a list of the things you are interested in (science, math, programming, human services, etc.) and then pick your top 2 or 3. Look to see what is common about those interests and then try to break them down to be more specific. Use the tools mentioned in the other answers to this question to add to your knowledge base and help make your decision.
Now that you have the information, you now have a place to start. The important thing to remember is that a "career", especially a "perfect career" is one that you are happy and satisfied with. It is not something that others tell you is good or bad. This is your decision and can be whatever you want it to be. Where you start may be a long way from where you end up, but it is the journey that matters. Your "perfect career" is one that you enjoy doing and can get satisfaction from whether others agree or not.
My "career" started in agriculture and has led me to computer manufacturing management. Not related except for all the steps in between that tied them together. It has been a long and challenging path but it has been a good one for me. As I mentioned earlier, a career is a journey and not a destination. It is something you work for but don't really see until it is done. The key is to do the best at whatever you do, use your skills and interests to guide you and then don't be afraid of change. Your interests will change over time and you will gain more skills as well. Don't lock yourself into thinking that what you decide on now is going to lock you into a rut. Be open to change and do what you are interested in and you will be successful.
Good luck in your perfect career.
Wayne recommends the following next steps:
Don't lock yourself into a single direction - graze widely across all the fields that catch your eye. If you're young, you probably feel like you don't have time to experiment with medicine and law and accounting and theater. You do, and you'll be a happier, more fulfilled person for having done it - which means you're more likely to find a great place to work.
Ceil recommends the following next steps:
Meet with people working in the different fields you're interested in. Don't be afraid to change of degree if it finally doesn't suit you. I've got two degrees in very different fields and I finally found the perfect job to combine both of them. Changing path should not be seen as a failure, you should look at it as an opportunity.
You should see which of the school subjects you are most passionate about and take examples of people who practice in the profession.
You can also do research of the different daily tasks they make, to be sure you will see yourself doing them on a daily , with passion and motivation.
My example: I liked mathematics at school, I looked at all the job that executed it (ex: teacher, administrator, accountant) and it was the accounting interested me.