Well, I've got a few things I've used to make super-duper-fast Shadowrun missions for pick-up campaigns; not quite the same as a one-shot because I don't have to wrap everything up at the end, but I've got a few quick things.
The Runner's Toolkit may be expensive, but it's got some stuff that's definitely worth it, including PACKS, which allows a degree of character customization without requiring too much system knowledge ("Veteran Gunslinger", for instance, is a PACKS module containing all you need to make a decent gunslinger). Chummer is a pretty good character generator for Windows that includes PACKS integrated, allowing you to churn out several generic archetypes quickly, whether for NPCs or one-shot PCs, plus you can then go in and fine-tune things. I've told newer players to use PACKS as a cheat sheet for what they should have on their characters to be well-rounded.
Make sure your adventures have everything ahead of time; there can be a cliffhanger in your one-shot, but you should try to make sure the players are engaged by the time it comes up, so you want to make sure you've got a general plan; I'd actually map out the scenario you want to use in real-time, allowing a bit of time for tangents and going off path, unless there's not much time allowed.
Calculate how long dice rolls take; I've found that in my group (horribly short attention spans accounted for), we can take up to thirty seconds to get all the numbers together to even do a roll (though if you're using pre-mades and have a reference copy that's great, though my all-digital bookkeeping makes it a mite of a pain), so I calculate combat length accordingly; I try to keep it just enough for everyone to get a taste of the action (so basically but wind it up in no more than five minutes. This means that I can have five different player rolls before getting the numbers down, plus narration, which puts a pretty big limit on how much stuff I can have, so I try to make combats end in the first or second combat turn, but still remain brutal.
I try to make the jobs something pretty simple; before they were made into super-actually-human entities, I sent players on ghoul hunts occasionally (though the more sapient they get the less tasteful I find making strictly antagonistically missions against them), but you could run into qualms if people don't like the subject matter. Basically, I try to make the job something people could have gone to a bulletin board and picked up (and we see stuff like that in-canon, which is a plus, though you do miss the Mr. J. aspect).
Another strategy I like is starting the scenario in media res, skipping all the getting to the location and the basic breaking in or the like (and giving problem/unimaginative players a guideline for what they should be doing, rather than gunbunny'ing) and putting them into the heat of action; for instance when I run the 3rd Ed. quickstart I would skip the whole Hans Brackhaus introduction and just put the players into their infiltration job, describing how they infiltrated the facility as the cleaning crew. Unfortunately, this can strip off a bit of the setting, but I've found putting in flashbacks or narrating the previous motives of the characters can put the mood into place.
Of course, I'm prone to using horribly short things as inspiration; I remember how the Shadowrun video game for Genesis would give you the occasional decision making snapshot where you got to choose from two or three options as events unfold, then immediately deal with any consequences (help someone for potential Karma, or let the people chasing them take them down and potentially do horribly nasty things to them), and I use them all the time, from someone offering grenades to the players for a miniscule fee but potentially being an undercover cop. This might result in stuff too short for a one-shot, but if, for instance, the players jumped the gun and did something they shouldn't have you could have them make up the rest of the allotted time running from KE or the Star.