The classical management functions are Planning, Leading, Organizing and Controlling. This misses something which I've found to be critical for my own work in this area: information-gathering. Managers make decisions about things that they don't have complete information about, and this predictably leads to crappy decisions in some cases.
A manager needs to obtain the right information. Usually, this isn't all the information, since that would be overwhelming, but a well-chosen sampling of the available information. There are vast arrays of Management Information (software) Systems available, of course, which generate all kinds of nifty reports and demand reams of input data in order to create them, but my point is more basic. Managers have to get that information, and if they only get it by seeking it out, they won't win. They need to educate and encourage their superiors, peers, subordinates, customers, and suppliers to bring them the right information at the right time, because they often don't even know what information they need to seek out.
It's easy to sabotage this. Shoot a few messengers, and nobody says anything about problems. Ignore the problems people bring, and they'll despair of getting any help and stop talking. This applies even if it's not in one's proper scope: ignore pleas for help at your peril. (The right response may be "Ask Dave; he's the guy for that." If Dave's technically the guy for that, but is a dolt who won't do anything, you can get serious brownie points with people by saying "Ask Dave first, because he's the guy for that; sometimes, though, Sue can help you out.")
Overfishing doesn't work in the long run: if people get too used to the Spanish Inquisition, they'll feel that they don't need to volunteer anything, because the manager would ask if he were interested, and the manager will eventually fail to ask for some piece of Vital Information. Plus, it tends to collect a great deal of useless, time-wasting information.
Information exchange is a good way to get this kind of ball rolling. Give people information which will be useful to them (without overwhelming them!), and they'll be much more likely to keep you in the loop. Giving them information, especially face-to-face, also provides an excellent opportunity for them to mention things.
Most managers know they need information, but few texts on the subject pay much attention to how they get it, particularly from other individuals in- or outside the the organization.