In addition to the specific Book 3 elements (gimmick, push, pull, enigma), here are some other ideas I've gleaned from roleplayingtips.com:
Know the Ending. Know where you want to take the adventure. What's the last scene you want in the adventure? Set that, then work it to there in the most enjoyable way you can think of.
Break cliches. Cliche helps understand the world, but good adventures take unexpected turns. So recycle cliches in unexpected ways.
(This one is more about refereeing: listening to good ideas the players come up with when trying to solve your adventure, and then spring it on them a bit later.)
NPCs and encounters are the backbone of every adventure. This is especially true when PCs are in a city -- the encounter table can be very useful here in mapping out a city! When creating an NPC, consider notes about her family and personal history, personality, "blind spots", and plans for the future. Quite often plotlines can be woven through these.
(Referee note, rather than Adventure Writing note:
My NPC method is to supply semi-random names on one sheet of paper for truly random encounters; I'll pick a name and assign it, crossing off the entries as I go, then note down the newly-created NPC on an "NPCs" page, leaving a couple of lines free for future notes.)
Vary the size and scope of plotlines (and secrets): mix up smaller ones with bigger ones, rather than progressing from small to epic (see dealing with the "cliche" above).
Don't bother much with prepared speeches by NPCs. Similarly, sketch out scenes, with just a few helpful details.
I love tangible things like maps, ship's papers, and the like. To be good for an adventure, though, it's often better to keep them enigmatic. This saves on prep time, engages the players' imaginations, and keeps the props themselves flexible.
Themes. Regina is a "capital world" -- so what might that mean? An adventure might describe the world using a color scheme, a particular way of designing buildings ("low-lying gravitic", or "solid and square"), a particular quirk of government ("each bureaucracy, strangely enough, performs the function of the
next bureaucracy down the list perfectly, but can barely execute its own mandate"), etc. Yori, on the other hand, might be a Baron's paradise, while still being mostly a gritty red-yellow wasteland. NPCs similarly can fall into themes, as can cities and starships (but remember the note on "cliche" above).
Environment and weather. Most versions of Traveller have rules for dealing with the environment, which can be seen as a potentially fearsome impersonal opponent.
Worry about the story more than creatures. Happily, that's more or less how Traveller rules spend their time: less on creatures, more on people.
Write down ideas while they're fresh. Move quickly on the good stuff, and toss the useless stuff. Then mull things over later.
Finally, for Traveller, this from Don:
Traveller is about travellers -- the name of the game is literally the role the game assumes for the player character. No matter what setting is used to run a "Traveller" game, there is a general assumption that there exists a class of individuals, from a wide variety of careers and social distinctions, who possess the ability to freely travel across parts of that universe, and the rules govern the exploration of those travels. Some within this class may be impoverished, and either work for their passage or steal for it, while others possess the ability to fund such travels in some comfort, and there are some who enjoy the highest luxuries while engaged in their travels. But the very nature of such travels breaks down social distinctions -- when problems arise, a real traveller is one who faces the moment alongside other travellers. Those outside this body of travellers can neither understand what would bring a scandalous rogue and the most noble Duke together -- but it is the shared experience of being a traveller which allows it to happen. Settings which apply this notion, and referees who indulge in this experience, take the Traveller role-playing experience to its highest levels. It is when an author or referee take their eyes off the travel, and focus on the story, that the game falters.