I've tackled this one before, I thought I was an F until I realized what it really means to be an F. After you've done something (almost anything), in that split moment after, what are you thinking about? -hang on, introverts think and then act - Well, scan your thoughts just before you go to action. If you consider how you feel about whatever it is you're facing, then you're an F. If you try to figure out how it works or functions, you're a T. The auxillary Ne then comes in and relates the data you've taken in to either a system of beliefs, or a system of logic.
oh, and you need to assess what you think of first. If you have any sort of balance, you'll likely exibit some kind of F thoughts after you've gone through T (or vice verse).