First of all, you can never plan ahead too much... Secondly, you can never trust your instincts and be open to possibilities enough...
These two are not mutually exclusive strategies but rather approaching the same "problem" from two different sides, and if both are done well, they feel like a natural extension of each other!
For example... I have roughly 3 days in Prague, the most heavily touristed capital of Eastern Europe. A Lonely Planet Encounter guide sparked my curiosity about its Communist history and Kafka's The Trial, so I started reading what is apparently Kafka's most famous work yesterday, and found a good book on the Velvet Revolution today. I would guess that I am now 350% more knowledgeable about Prague than I've ever been, even though I haven't finished either text, and there's actually a long way to go until I do. I'm pretty sure that Kafka is studied in detail in Czech high schools, and in even more detail in universities - after all, he's their most famous author! So not only does the work give me an insight into the mind of an articulate, moral and eminent figure, it allows me to better understand the average Czech person who regards Kafka as part of their literary heritage.
In the tiny Encounter book (which I am reading one month before I'm due to leave for Prague) I found out that Wenceslas Square had been a gathering place for dissidents, and still the Peter Sebesteyn history book gave me the details which gave rise to this generalisation, such as the supposed death of a maths student during an unorganic student protest has given me an entirely new reason to visit - details vivid and vague have captured my curiosity, so I am likely to delve into the subject until I can't delve anymore...
This is all great, but it's only a beginning; I want to memorise street names, bus numbers, opening hours, and all sorts of details which will help me create seamless transitions from one place to another. I want to know how to get from one place to another in the cheapest, quickest and most comfortable way, because if I don't focus on these things now, I'll be focusing on them when I get there, and the less I need to concern myself with practical details, the more I can drool over the architecture or watch the people as they stride past.
(The sort of practical details I listed just there can quickly become part of your conceptual knowledge. For instance, knowing what all the major tourist sights are, even if I have no intention of going to all of them, allows me to assess what kind of visitor comes to Prague, and will help me analyse every visitor I see with greater nuance.)
Some people may claim that it's dangerous to plan too far ahead, but all you are doing is increasing your awareness, not pinning yourself down. Just because you know a train is available, doesn't mean you're going to take it at any cost. It does, however, make you flexible and confident once you're there. Remember Foucault: Knowledge is Power!
Knowing that the buses are running until the early hours of the morning (in general) means that you can relax and talk to that friendly stranger at the bus stop for longer without worrying about being stranded far from your hotel. The hypothetical friendly stranger may then decide to show you a side of Prague that is not part of the Lonely Planet tourist itinerary, but is just as revealing, amazing and fun. The next day, you can hypothetically pick up where you left off, all the more awake to the beauties of the place.
Today I decided to dine in a restaurant that served Korean food, and had some lovely Japchae with Wagyu beef. It was the first time I tried this dish, but it won't be the last! Now, when I stop over in Seoul on my way to Prague, I know at least one dish that I can safely order without choking over the spiciness of its contents! (I want to like spicy food, but my system hasn't yet caught up with my mental openness to chili!) I guess I'm lucky that you can find just about any kind of cuisine in Sydney.
Perhaps best of all, I told my waitress that I was interested in all things Korean and she was kind enough to leave me her email, in case I had any questions. I told her I would think of some things to ask her, and look forward to learning about Korea from an insider.
As if on cue, Richard Florida published an article yesterday on Korea's prospects in the future, praising its innovative technology but pointing out that 40% of Koreans hadn't had a conversation with a foreigner in 2006, and the more lucrative it could make itself to foreign creative class members, the higher its levels of prosperity would reach. All of these things help me create a sense of place, for better or worse: it's something to approach the concept of Korea with, ready to be improved upon, or altogether transformed.
It's not often you fly from Seoul to Prague - though part of two prosperous regions which attract a lot of visitors, Seoul mainly attracts businessmen and Prague is not as popular as Berlin or Vienna (I think... wait, I'm assuming. Let me know if it's otherwise!). I'm enjoying the offbeat-ness of my itinerary. In fact, only Berlin will be a super-popular destination of the places I'm going to - Copenhagen, Helsingor, Malmo, Gothenburg, Stockholm and Uppsala are still not mainstream European destinations, although I hear they will attract their fair share of visitors, especially in the capital cities. One exception may be Roskilde, which I will be visiting during its eponymous Festival - seeing as this is the biggest musical festival in Northern Europe, I expect some version of 'a big crowd'. (Note to self: Get to the stage Robyn is playing at early!)
Anyway, I am doing less planning for Denmark and Sweden because I will be shown around by friendly locals, and being with them means bypassing all the typical tourist delays, mistakes and head-scratching. I do have vague back-up plans just in case something happens and they can't make it anymore, though.
I was a Girl Guide for a year or so, and the motto 'Be Prepared' - so rarely evoked is my GG membership in any context that I am surprising myself here - comes to mind... when you are as prepared as possible, being at your most open to improvisation is easiest to achieve. Sometimes planning for improvisation doesn't go all the way - being creative with options is far more effective when you have the knowledge to be resourceful with.
At any rate, no matter how little or much planning you have done, you may surprise yourself by how much you can learn about a place just by walking down a street or watching a group of people socialise with each other. In the event that I'm not as prepared as I'd like to be, I do my best to pay attention to everyone and everything, and hope I will get swept up in the magic (or self-perpetuating vibrancy, if you like) of the eyes of another waiting to be found by those that dare imagine its theoretical existence.