How To Run A Successful RPG: Some Tips

Thinking about gaming, I’m just sort of putting down some random rules I have as a GM that make for better play:
Make Sure Each Player Will Have Something To Do.  
Some of the most frustrating games I’ve been in were where I told the GM, “I want to play a sniper,” and all of the combat turned out to be in hallways, leaving all my skills to atrophy.
As a GM, I’d be loathe to let someone play a sniper – it’s the kind of role that invariably involves splitting the party, and it’s hard (not impossible, just hard) to come up with consistently interesting combat challenges for someone who works best from half a mile off.  But if you’re going to tell someone, “Okay, put all of your points into ranged attacks and a weapon with a slow reload skill,” then you owe it to them to put them in a situation where they’re often going to be useful.
It’s way better to veto a player’s choice than to get them all jazzed up for playing a ninja, only to discover this isn’t really a stealth game.  If you give someone a skill, make sure they have regular opportunities to use it.
Give Each Player A Clear and Unique Role.
There’s a reason the classic D&D party is a Fighter, a Mage, a Cleric, and a Thief.  It sounds good, having two sword-swingers around, but the danger of imbalance becomes clear very quickly.
See, if one of the swordsmen gets notably better at something (due to levelling up faster, or better weaponry, or better stat-whoring or whatever), then suddenly as a GM you have this situation where you’re stuck with one of two challenges:
* Make it challenging for the big tough guy, at which point the weaker character is helpless.
* Make it something the weaker guy can handle, at which point the big tough guy eats his lunch.
Plus, when you run into the inevitable “Ah ha!  This monster is invulnerable to swords!” then suddenly half your party’s sitting around with their thumb up their ass, completely helpless, which is frustrating.
This is not to say you can’t have multiple fighters – but have them serve different roles.  Maybe it’s Mace-Man and Sword-Woman.  Maybe it’s Crazy Barbarian and Nimble Fencer.  But find some way so that their roles in combat are different, and that they fight the enemy in very different ways.
Avoid The Roll-Fest.  
The most boring combats I’ve ever been in involved the times where I realized I had no other tactical choices but to keep attacking with my main weapon and hope I didn’t die before he ran out of hit points.  At which point the excitement of combat boiled down to this:
“I roll an 16.”
“You hit and do 8 damage.”
“I roll a 7.”
“You miss.”
“I roll a 14.”
“You hit and do 12 damage this round.”
That’s not roleplaying, that’s math.  What you want is to provide characters with multiple workable options in combat, where taunting the bear to draw its attention or trying to trip it into a pit or rolling a boulder onto it are all options.  Once your players realize that there’s precisely one way of doing damage, then it’s all about the dice.  And the dice are the most boring things about your game.
The best way you can avoid the roll-fest is to:
Treat The Environment As Another Enemy.  
DMs spend a lot of time statting their enemies, but with every session you should think of the terrain they’re fighting on as another potential villain.  Fighting on a flat plain with nothing in sight is not only visually dull, but it’s tactically barren.  When you’re in the arena, your only choice is to close in and fight.
So why not have them fight in a maze of steam-filled pipes, Empire Strikes Back-style?  How about fighting in the middle of an avalanche, or on a set of rocks teetering over a pit of lava?  One of the most memorable games I ever ran involved a castle that got teleported into the upper atmosphere, and the characters had to fight in free-fall as the hallway plummeted to the earth.
Always have something interesting at hand during combat – innocents to protect, things to grab in combat as impromptu weapons, places to hide, items to blow up.  The reason Raiders of the Lost Ark is so fucking awesome is because every action sequence follows this rule.  You do likewise.
Conversation Is Combat.
If you’re going to have NPCs talking to players, give them a goal to accomplish that they get in and get out on.  Hands-down, the most boring games I’ve been in were where the GM had dudes come in and ramble at us for an hour at a time while we tried to guide the conversation in the right direction, only to learn that there was really no point in running into this yahoo.
Which is not to say that conversations should be quick – you can have some really fun things going – but in combat, the villains have a clear goal: kill the intruders, drive them from their temple, escape with the foozle.  Your conversations should have a similar goal: get the PCs to help them, deliver a piece of much-needed gossip, try to seduce a player in five minutes or less.
Give them a clear goal so that you can have a sense of rhythm and ramping to each discussion.  Also see: The King’s Speech, which has some delightful fiery interplay between characters who want very different things in every scene.