The best thing to do is to analyze your habits, where have you always found yourself to be? For example, I always found myself looking for opportunities and generating a multitude of different choices to select from. Because I noticed this pattern I entered into Sales+Marketing. More specifically I noticed what I personally had the most fun doing and what I also had the best results with was lead generation.
A lot of success in a particular industry has to do with personality type. Someone who does not like to read or stay in one spot for a very long time should not be a contract lawyer, just like someone who despises physical activity should not be a professional athlete. You do not need to love something to be good at it, but you have to ask yourself... am I willing to stick through the tough times in order to bask in the good times? Is this something I am committed to?
With this approach you can then narrow down some of your patterns, behaviors, and thinking styles into niches which are clearly more favorable for you. From there it is a lot easier to ask others and interview, or just jump in and test a multitude of different scenarios and make a choice.
Hope this helps, thanks.