In order to determine what makes a DM, one must first consider what makes a player INTO a DM. Does the drive to run games come from an innate, frustrated, power-hungry desire to manipulate and crush other players, or does it come from a combination of the urge to create, plus the urge to entertain the storytelling possibilities of RPGs and foster them in the minds of others?
If you are of the former category, well... at the very least you will serve to season your players for tough times, and those whose curiosity survives your malevolent attentions will forge on to become truly magnificent players in their own right (albeit likely not as members of your group)! If you are of the latter school, then you have found fertile ground in which to plant your creative uh, er, seed.
For myself I hang between the two worlds. I like story, but I like gripping, edge-of-your-seat action as well.
I started as a player in 1980. I coerced my mother to pick up a copy of the 1st edition Monster Manual and pored over it for weeks, enthralled and mystified. The next year I spent a summer in Ames, Iowa running around with a bunch of other tween miscreants. I believe the very first RPG I played was Traveller and I can't recall the story but involved some ATVs, a weapons cache, and a whole lot of shooting in the desert. The next game I played in was White Plume Mountain, and I ran 3 characters. I tended to run one character at a time until they died, which was frequently.
The very next game night after that was an adapted version of the dungeon laid out in the Dungeon Master's Guide, in which plate mail-clad gnolls were firing 'magic missiles' from their crossbows, wiping us out immediately.
Each game ended in a TPK, but I didn't care. I was hooked. Every summer I spent in Ames afterward I headed up to the RPGA night at the student union and met up with my comrades and others to play.
In junior high I joined a short-lived D&D club at school, run by Mr. Day, the Cool English Teacher. This was during the Satanic Panic of the early 80s, and I suspect there was some pressure from school admin to shut it down, and so they did. Later in high school I found a group of gamers amongst my peers, whose over-the-top games made of a mish-mash of various systems are still some of my best gaming memories.
I took my first stab at running a game a year or so out of high school. It wasn't very well thought out and only lasted one night, but in retrospect I think I learned a lot from that ephemeral campaign. Using a standard 1st edition D&D rule set and some blotter-sized graph paper, I scribbled out a large scale map. I constructed a loose setting involving a long sort of spice road travelling through unsettled or unknown lands. I then constructed three new races to introduce some complexity to the situation.
One race, a sort of improved human race based on the Ogre race from Runequest which I called "sin eaters"; recent arrivals from another plane, all carnivorous zealots, but following an alien branch of lawful good alignment whose strict belief system only allowed them to consume the condemned. This structure made them zealous pursuers of evil, though perhaps a bit too zealous, depending on the situation... I thought encounters with this race would provide an excellent moral foil for anyone playing a stridently aligned priest, monk or paladin, as well as a frightening challenge for less morally adept players.
The second race was a malevolent race of elder wizards slowly emerging from the sealed ruins of their ancient ziggurats. They had been my human answer to the drow; not dark skinned and debased, but cold, calculating overlords who were disinterested in the surface world except as a possible source for slaves or trade.
The last was a feral race of sentient feline humanoids who ended up fouling the whole campaign. I gave them too many bonuses in the form of stat adjustments, claw/claw/bite attacks, and rear claw rakes (thinking that I was balancing out the lack of useful hand weapons and armor). HA!
This initial version of the campaign lasted all of three hours. My players, savvy power-gamers who saw the opportunity to press an advantage- chose to toll up cat people and commenced to slaughter every human they ran across. No time for plot - every humanoid within bat-swinging range immediately went down under the merciless claws of the power-mad players.
At a loss for how to continue the game I chose to reboot it instead. I disallowed the home brew races as player characters and cracked open the Village of Hommlet. I added a few more players, including a couple of players' girlfriends (almost always a good idea for reasons I'll get into in another article), and we had a blast running through VoH and the Temple of Elemental Evil up until the group dissolved a few years later when half my players relocated.
1. Playtesting is a good thing. Even if that isn't possible, at least run your ideas by another GM, preferably one with more experience. It doesn't hurt to get a second opinion. Creativity is good; unbridled creativity can upend the entire game experience.