My group actually deals with this a lot. We've been getting looser on the storytelling, and moving much more into campaigns where very little is planned. Theres is a setting, some kind of antagonist, and a vague idea of the end of it. From there, the players get dropped somewhere, and then meander about, following whichever breadcrumb trail intrigues them the most.
The way we tend to handle this is treating it like the old saying, "All roads lead to Rome". Theres a beginning, and there is a destination, but no one knows what will happen on the way there. Theres a good one or two encounters planned ahead of time, that the party will reach through there own means, with any other encounter happening on the volition of the party. And if the party does something crazy on their own, I adapt the campaign to it. The less of a set plan I have, the more fun it is for me and for the players.
As for DMing, its very much a practice thing in my eyes. I come from a group that had only one experienced DM at the time. He was a master at baiting, and railroading in such a way that the players barely noticed. It was there, but there was always player incentive to follow along. That DM left after the first 4 years do to college, and we got another skilled DM then. He was the opposite, and is the person I take my running philosophy from. He has a beginning, a vague end, and will re-write parts of the campaign based on what players come to him with in their characters.
Over those years, I had tried DMing to very little success. My first campaign, with 2 years of experience role-playing, I kept switching between too loose and too controlling. As a result, the characters had no reason to follow the plot or to deal with the antagonist, and ended up sinking a small continent. My second campaign, with 6 years of experience role-playing, I was a bit too loose, and lacked the world for the players. I was on my heels far too much, and it ended prematurely. As for my current attempt, with 8 years of playing, it is going well, but I still have a ton of room to improve. It is open, in a developed world. The players have incentive to be interested in the antagonist, but are also very driven by their own personal goals in the world, which is a good medium for me right now.
/ramble