JMD (who, by the way, is one of my absolute favorite people I've met on the forums - he's the mad genius doing the GURPS Calculator) started this thread asking about why people don't like GURPS. If you can read through some of the bullshit, check out the Reddit thread. I rather like this little gem, because it sums up what I've been able surmise on the issue myself.
Because the idea that you don't actually need any of the rules beyond "roll 3d6 under your stat to succeed" isn't telegraphed very well and people end up thinking that you need the super-complex stuff to have a game of GURPS and that just scares off everyone.
When I ran GURPS Dungeon Fantasy at ROFCON I had decided early on I was going to under rug swept everything possible. I didn't want the players to see the versatility of the system by looking at the sheet. I wanted to show it to them while we played. I wanted it to be lightning fast play, but also (not so) subtly pointing out its strengths. Considering I got three players from that game into my permanent gaming group, I think I succeeded. But how did I do it? Was there some scheme involved? Does the Devil look after his own? Or am I just that personable? Well, Big yes to the first, small yes to the second, and so I've been told on the third. At my very core, I am a teller of tales and a spinner of stories, but I had a plan from the very beginning. This is how I did did it:
One on One Teaching
I sat down next to each player and explained to them every line of their character in as much depth as I could shove in 20 minutes. I asked them questions and I got them to ask me questions. I pointed out acronyms and let them take notes. I gave them a quick idea of what needed to be done to play their character.
Real World/Popular Culture/RPG Examples
When I explained the characters to their players, I did it in terms they could easily understand. "Your character can do a cling/pull of over 400 lbs." "Your skill with a sword is at the once in a generation level." "Higher Purpose (Slay Elder Things) is like DnD Favored Enemy." "Your ability to command skeletons is like a Diablo Necromancer." and so on. If you can make those connections you've just done half the work.
The Low Die, Riders a Little Higher
GURPS die rolls is summed up thus: roll low for everything, but damage and reactions. That's it. Us GURPSers know that...but it's hard to understand for some people because nearly every game system out there is "roll high." Because of this I suggest you often repeat that little mantra. "Roll low for everything, but damage and reactions." When a newbie asks you what they want to roll for their Broadsword skill reply ""Roll low on your Broadsword skill, but high on damage." If you do it enough, they'll get it. When they stop asking you what to roll is when you stop repeating it.
Sure, There's a Rule For That
"I want to [insert whatever request], how do I do that?" To which you reply: "Sure, this is GURPS, it's kind of like the RPG smartphone because there is a app for that. And by app, I mean rule." Seriously, this must have happened a dozen times at the table and every single time there was something covering the situation or enough of a rules extrapolation to cover it. Now, I won't lie, this takes a GM who knows the system forward and backward, but if you're familiar enough with GURPS and can do this it WILL win you converts. Even if you are not that familiar with the GURPS system the rules for Roll and Shout! (p. B497) apply here - even in a cinematic game. If you get bogged down by looking for rules the game will stall and you must prevent that no matter what.
Pretend like you have 4 hours to stop the terrorist attack from succeeding and focus. Help the others focus too. If you let a player's attention wander too much the game will bog down and as I've said before YOU CANNOT LET THAT HAPPEN! The terrorists will win if you do - so don't.
Let the Players Be Awesome
Don't say, "No, you can't do that." Say, "Sure, but you'll be at a penalty." In short, let the players be awesome. Some might see this as the players "winning." It's not. It's about letting them shine at the things their characters were built for. Don't punish them because they want to do something that they weren't build for. Encourage them to try new things, but let them know ahead of time it might not work. Taking risks and being rewarded is one of the most satisfying things you can do in a game and it's those experiences that stick with a player the most.
Make It Interesting
Above all remember these three worlds: Make. It. Interesting. Be enthusiastic! Be happy you're there. Let them know that you are happy they are there. Because, damn it, you should be. Let them know that their character actions are cool. But more than that, run your game the way you would want to play it.
Picking Over the Bones
I'm sure I could come up with a few more, but that's what I went into the Con with. Most of this stuff is pretty common sense if you think about it, but getting it codified and laid out can help. What sort rules do you have for yourself when introducing newbies?