Madhatter-
I know that I am a little of everything, so deciding what I am was never an issue, but I will offer this advice: read, read, and read some more. On the forums, stories online and off, non-fiction books about BDSM, and then think about what appeals to you most. Also, something lots of people will tell you here, talk with your partner (and then talk some more--then try stuff!) Ozme has suggested to me that I keep a journal, even though my lover/Master does not ask it of me, just to sort out my own thoughts. Maybe even, without worrying about grades or grammar, include "book reports" on what you read, noting what you liked and what you didn't. This can lead to a list of things you would like to try that you can share with your partner-trading those lists is a great way to start a conversation, and there is nothing wrong with trying both sides to see what you really enjoy. There is a great thread in the switches section, with a title about people looking down on switches that has a lot of really good stuff about being top or bottom or both.
Hope this helps.