Some high (or low) points of my 'style':
1. I don't plan a campaign arc from start to finish. I let things be more sand-boxy, in general terms. I know where the campaign is going to start, but not where it's going to end. The BBEG is going to depend a good deal on where the players go, what they do, and the cages they rattle. I like the idea of lower levels = local heroes, medium levels = influencing the life and times of the setting, high levels = protecting the world or the plane from external threats. I don't run campaigns where the PC's are overtly evil with evil goals. This whole approach is why my hands-down favorite place to run a game is the World of Greyhawk. In fact, I don't think I've DM'd a campaign anywhere else since the 1980's, except for dips into Dragonlance and Ravenloft.
2. I try to put in as much prep time beforehand so that I'm not having to flip through books / tabs and generate stuff on-the-spot in game. It also allows me to tailor encounters and such (to a degree) to the group, although I like to leave in surprise elements for them along with the occasional too-easy or too-hard encounter, as the dice decree. If I know they are going to be traveling cross-country for a portion of an adventure, I roll and pregenerate the random encounters, weather, and all that stuff so that it is ready to go and I don't have to pause play to generate it on the fly. If the players do something that takes them off this 'script', such as it is, I'll adapt as necessary or go to random generation on the fly, even though it slows things down a bit.
3. When the players finish an arc or an adventure, the choice of where to go and what to do next is up to them. I'll usually set adventure hooks for them to choose from, and what they pick is the path they take next session. There's usually an understanding between myself and the group- because I do so much prep between sessions, once they pick something they generally stick to it, lest they throw things into total disarray. Stuff happens sometimes, though.
4. I usually roll behind the screen as DM, and sometimes I will have players make rolls that will have no effect, but it keeps them from that metagaming situation of 'he's making us roll so there is definitely something there.' More to the point, they know I do this with the 'random rolls.' I generally don't fudge any roll other than something that will obliterate a PC and disrupt the game, but that is not to be taken to mean that there is no danger. PCs can and do die in my campaigns, but occasionally to keep a story moving I'll show a smidgen of mercy that they never see, like maybe dealing normal damage on a monster crit instead of doubling it. That said, my monsters act and fight to the utmost of their stats, and the players had better be smart as well or perish. Play stupid games, win stupid prizes. As I've mentioned in other threads, trying to negotiate / deal with evil monsters and humanoids usually ends badly for the party. They may achieve a temporary advantage or goal, but evil creatures betray. It's in their nature.
5. I've noticed in some games that players tend to take treasure on the spot as it's found. Since I've played as a kid, I've always encouraged a 'treasure kitty' during any given adventure, and the divvying of stuff that is not immediately useful or obviously useful to a particular class of character (potions, scrolls, etc, or magic weapons) is handled at the end of the adventure. Gems can be sold and money divided, or treasure partitioned into relatively equal 'shares' from which the players pick what they want between themselves. I DO NOT encourage PvP sort of play, or the party rogue stealing from his/her friends, etc, but I don't forbid it, either. It's their game, and if they want to engage in self-destructive behavior I sit back and let the chips fall. When it ends badly (as it often does), I simply point out that this sort of play is generally detrimental to a fun game, but it's up to them. The other advantage of a treasure kitty is that it gives players a choice to make: do party 'expenses' come out of the kitty before the profits are shared, or do they share beforehand and each player is responsible for his or her own expenses? For example, the party wizard has a lot of upkeep expenses for those spellbooks, etc, from which everyone benefits in the wild. Again, up to the players.
6. I do the occasional voice for the NPC's, most often if I'm going for a laugh. My voice-acting skills are somewhat lame, however, so for the more mundane stuff I'll often revert to third person narration. "The inkeep says he has no private rooms..." sort of thing.
7. I do like to keep combat spicy by narrating the outcome of actions. Critical hits get big hand motions and visceral descriptions of monster dismemberment, and so on. I've found players dig this, and I like having them describe their own kill-shots and stuff as well. I enjoy it, too.
That's a general overview of how I conduct a game.
