There are a number of posters who don't seem to have internalized the fact that there are many ways of DMing and playing D&D (or any rpg), and that what's really important is that everyone involved has fun.
My personal style of DMing has evolved over 35+ years. At one point, though, sometime in the mid-80s, I found the style that suited me best, both in terms of my enjoyment and that of the types of players who usually gamed with me. I have tweaked it over the decades and adjusted it a bit to suit different groups, but the overall gist of it hasn't changed much.
At it's most basic level, I tend to DM this way:
- I design my own world and adventures. That keeps the players from using knowledge they gained by reading published books, and allows me full creative freedom. For me, the design aspects are half the fun.
- I follow the old school D&D philosophy: if there is a rule that I don't like, I get rid of it or change it. I don't do that on the fly or capriciously. That allows me to present game the way I like, and discourages rules lawyers.
- I don't allow rules-lawyering in my games. If I make an obvious mistake, I want someone to point it out to me, but that's different. I don't expose the background mechanics in my game - players don't always know why I'm rolling, the exact AC of the creature they are fighting, etc.
- I allow min-maxing, but the characters have to deal with the consequences of the "min" part. Given that, most of the players don't choose to min-max.
- I don't allow electronics at my table. Players don't get to text or play with their cell phones without a good reason (keeping an eye on their kids, for example). If the player can't stay relatively focused on the game, (s)he won't fit into my campaign.
- Though it's natural to make jokes and have fun at the table, I don't allow players who are mainly there to socialize or spend time with their significant others. If the game isn't the main focus, that player doesn't need to be there. I don't have a lot of time to game each week, and don't want to waste it with people who would be just as happy chit-chatting in the mall food court.
- I don't have a big ego. I don't think in terms of players outsmarting me, or see myself in opposition to the players. I want them to have fun, be creative, and enjoy the fruits of their accomplishments. I'm primarily there as a facilitator.
- Players only know what their characters would know.
- Rolls count. Without any potential consequences to decisions, the game ceases to be fun. Players have to live with the results of their choices. Having said that, I only require rolls on things that can't be resolved through roleplaying. For example, if a character wants to try to talk an NPC into doing something, I go through the conversation with the player, with me playing the role of the NPC. I play the NPC to character - each one has unique motivations and personality. We don't just do a simple charisma or bluff roll.
- Characters can die if they make bad choices (ex. attacking something they know they can't possibly defeat). The game is less interesting if there isn't a chance of death in combat.
- In general, the only time I fudge results to keep a character from dying is if I realize that a character died because I made a poor decision in designing the encounter, putting the group in a no-win position. That has not happened many times over the past 35 years.
- I encourage and reward creative solutions to difficult problems. In fact, I never design a campaign or encounter with only a single path to resolution. I make sure there are many ways to approach it, and particularly enjoy it when the players find a way to resolve things that had not occurred to me. I reward that with extra experience points.
- I reward players who come up with long-term goals, hobbies, etc. for their characters, and follow through with them over the course of the campaign.
- I design a world littered with various opportunities for adventures, encounters, etc. I make sure that the characters get wind of those things at various points, and offer them reasons to pursue them, but they don't have to do that. We can go full sandbox mode if that's what they like, because I have fully populated the world long before we start the campaign. Most players prefer to pursue adventure hooks, but some groups want to pursue their own goals. I can go either way with them.
- I don't run one-off games in D&D or Pathfinder. I run campaigns.
- Combat is only one facet of my campaigns. Characters generally spend more actual play time doing things that don't relate to combat. I know how to keep that sort of thing interesting.
- I don't play with alignments in general. I do require the players to come up with personalities for their characters, though, and reward them for sticking to the character concept. I have never had an issue with that approach. Clerics and other deity-oriented characters have to stay within the general scope of what the deity allows, though.
- PCs can be "evil" by the common conception of the term, as long as they are motivated to act cooperatively with the group. That's not much of a stretch in the real world, even, particularly given the number of CEOs and politicians who are effectively sociopaths.
- Just like PCs, NPCs are individuals with their own personalities. Not all NPCs of a particular species fall neatly into stereotypical concepts of "good" or "evil." Some do, some don't. Even creatures that are by definition "evil" (demons, for example) may express their alignments in different ways, and ultimately most have their own sense of ethics, however odd they may seem to humans. That sort of thing encourages the characters to interact with NPCs as individuals, not as cookie-cutter two-dimensional things.
- Players can use almost any class - including third-party ones - as long as they fit within the world I designed and are not overpowered. I will even work with a very motivated character (outside of game time) to create a new class that (s)he has envisioned, as long as it fits within the game.
- Players can have characters of any species, even those that are not officially playable, as long as they fit into the world I designed and are not overpowered. As with original classes, I will work with a motivated character to figure out the applicable ability scores and traits. The character does not have to be of human-level intelligence, but does need to be intelligent enough to learn and make decisions that aren't purely instinct-driven. Given that, a dog would work just fine, but an ant wouldn't.