One type of information dump, most commonly associated with sci-fi, and certainly present in fantasy is the situation where the writer feels the need to provide an explanation of how something works. Depending on your circumstances this can be really hard to deal with. I think the expectation in sci-fi is to provide at least some explanation about how certain technologies work. After all, that’s basically the premise of the genre. That said, billions of people across the planet use cell-phones every day and only a tiny fraction of them know how they work, outside of routine cell-phone maintenance, the only other detail most folks are familiar with is the need for a cell-tower. It seems to me that this could be a pretty good rule of thumb to follow when thinking about how much detail a reader needs. Of course, if your protagonist is a cell phone tower engineer, all bets are off. To give another example, think about Star Trek vs. Battle Star Galactica (the new one). In Star Trek we learn all about tachyon beams and anti-matter mixtures in the warp core, but I don’t recall ever meeting a single FTL drive engineer in BSG. These examples, I think, really illustrate well done instances of including a lot of information or not and the types of stories that work with each situation.
For fantasy, we run into similar sorts of things. For example, how much does one explain about the mechanics of magic? I really don’t have a good rule of thumb for dealing with this, except to say that you can write a really good story without many details (Harry Potter is kind of like the cell-tower example, all we really know is that witches and wizards can do spells and need a wand). I spent a lot of time agonizing over how much detail to give in the description of how magic works in my story. I made up a lot of rules too. In the end, I decided to try and provide few details, instead focusing on the effects of magic, including both the outcome of the magic as well as the physical effects on the one performing the magic. As I’ve gone along, many details of how it works have been described, but only out of necessity. For my story, I think that works pretty well, but like anything, I suppose it depends on what you’re trying to accomplish.
If I were to try and give advice on this I’d say put in the detail as you write. Then, as you begin the process of revision and polishing, you can focus on removing stuff that doesn’t really help the story in some way. Sometimes, all your getting from a description is setting, and that can be good too.