Generally speaking the fool is about the beginning of a journey - the start of new things, infinite possibilities. With this thought comes the idea of a warning, of keeping your surroundings in mind lest one step off the edge, fall and end up looking like a 'fool'. It is about keeping perspective and some reality around you while following this path.
The journey is usually something that is anticipated with some enthusiasm and a feeling of being free. It is a childlike excitement, one that must be tempered with wisdom from some source (a friend, your inner voice, etc).
Of course as with all readings of cards one must take into account the question, the surrounding cards etc in making an interpretation, these are just generalities.