As others have said, the important ones are:
*Locals without a quest. Have them stumble across dungeons or ruins and other similar things - give them a feeling that the world exists beyond just them.
*Diversity. Nobody wants to do quests in Ye Old England forever.
*Multiple incentives. Don't just give one hint that there's cool stuff in a dungeon, give several!
*Don't go overload on the fluff.
I'm going to add two here:
*Players can make their own stories. Why is this linked to MMORPG? Ultima Online was HUGE for player-made content lore, stories, cities, etc, with there being almost no "official" player-made content. A cruder version exists in most RP servers in most other MMORPGs. Let players make guilds and gather NPCs. Increase their foothold and input into the universe. Maybe in Heroic they have a house, in Paragon they have a guild, and in Epic they have a kingdom (Screw around and raise/lower the stakes as you see fit).
*This is in direct opposition to your DMG, but make other adventurers. Even if your story has your players as THE ONLY ONES THAT CAN STOP HITLER MCNASTYSTALIN'S DOOM FORTRESS, make other - if lower level/power - adventurers. It gives the PCs a sense of ranking. Maybe when they start, the other adventurers they meet are obviously more powerful. Later on though, they're the strong ones. And of course, having other groups of adventurers gives more reasons for them to make a kingdom/guild/mark on the setting. How bad is that BBEG? He just ripped the heart out of that warlock you were buddies with! How powerful is your influence? Several adventuring parties are now going out with you as their role model! Furthermore, the other adventurers increase - not decrease - the sense of excitement and discovery. If you are literally the only other adventurers, then it's not very exciting to keep trippping over forgotten tombs. But if you're one of many groups, you're not just "the crazy bloke who goes into the woods," you were the group of adventurers that found and defeated the Lich of Toomanyvowels is in the Tombs of Evilsoundingnoun. You aren't the only adventurers out there - but you are the ones that did the good deed. And next time you hit the tavern, those other adventurers are going to be eagre to hear your stories.
And here's something to ignore from MMORPGS:
*Never go back to the last hub
No. Do not do this. Do not fall into the trap of "WELL WE USED UP THIS TOWN FOR IT'S QUESTS, TIME TO MOVE ON AND NEVER RETURN." Let your characters make an actual HQ. Sure, they have to go out to their adventures, and maybe have a small village or two that needs some evil butt kicking, but then something like "DEMONS ARE ATTACKING OUR HEADQUARTERS!" or some other big thing can bring them back to a town/city they've invested a lot of time and emotion into. It makes them care more.
*Locals without a quest. Have them stumble across dungeons or ruins and other similar things - give them a feeling that the world exists beyond just them.
*Diversity. Nobody wants to do quests in Ye Old England forever.
*Multiple incentives. Don't just give one hint that there's cool stuff in a dungeon, give several!
*Don't go overload on the fluff.
I'm going to add two here:
*Players can make their own stories. Why is this linked to MMORPG? Ultima Online was HUGE for player-made content lore, stories, cities, etc, with there being almost no "official" player-made content. A cruder version exists in most RP servers in most other MMORPGs. Let players make guilds and gather NPCs. Increase their foothold and input into the universe. Maybe in Heroic they have a house, in Paragon they have a guild, and in Epic they have a kingdom (Screw around and raise/lower the stakes as you see fit).
*This is in direct opposition to your DMG, but make other adventurers. Even if your story has your players as THE ONLY ONES THAT CAN STOP HITLER MCNASTYSTALIN'S DOOM FORTRESS, make other - if lower level/power - adventurers. It gives the PCs a sense of ranking. Maybe when they start, the other adventurers they meet are obviously more powerful. Later on though, they're the strong ones. And of course, having other groups of adventurers gives more reasons for them to make a kingdom/guild/mark on the setting. How bad is that BBEG? He just ripped the heart out of that warlock you were buddies with! How powerful is your influence? Several adventuring parties are now going out with you as their role model! Furthermore, the other adventurers increase - not decrease - the sense of excitement and discovery. If you are literally the only other adventurers, then it's not very exciting to keep trippping over forgotten tombs. But if you're one of many groups, you're not just "the crazy bloke who goes into the woods," you were the group of adventurers that found and defeated the Lich of Toomanyvowels is in the Tombs of Evilsoundingnoun. You aren't the only adventurers out there - but you are the ones that did the good deed. And next time you hit the tavern, those other adventurers are going to be eagre to hear your stories.
And here's something to ignore from MMORPGS:
*Never go back to the last hub
No. Do not do this. Do not fall into the trap of "WELL WE USED UP THIS TOWN FOR IT'S QUESTS, TIME TO MOVE ON AND NEVER RETURN." Let your characters make an actual HQ. Sure, they have to go out to their adventures, and maybe have a small village or two that needs some evil butt kicking, but then something like "DEMONS ARE ATTACKING OUR HEADQUARTERS!" or some other big thing can bring them back to a town/city they've invested a lot of time and emotion into. It makes them care more.