Here's how I usually do it. I will include examples based upon my own group.
1. Look at the players in your group and think about what they like, and what kind of run they would like to do. Pay attention to their individual likes and dislikes. Some of this information can be gathered by looking at their characters too. Determine what the team might be good at, and make notes of what each of their specialties is. Think about how each team member might be able to grab the spotlight for a bit. Finally, look at their contacts and determine who they might hear about the job from. This can be your normal fixer, or could come directly from the source (like if the character has a mafia underboss as a contact).
Some of the things my players like are action movies, fast cars, and gambling. The players' characters are as follows:
- Human "Ninja" Bounty Hunter. Mundane, and has no cyber other than wired 1. Proficient with pistols and smg's but not extraordinary. Good in close combat and stealth/athletics. Has close Yakuza ties/contacts.
- Dwarf Aspected Magician "Fire Mage". Has extensive burn scars over whole body, is struggling to maintain sanity. Member of the Halloweeners gang plus contacts in gang.
- Human former low-level bodyguard. Mundane, has cyber-replacement foot and (arm too I believe) due to accidents. Boosted reflexes 1. Recovering kamikaze addict. Was essentially hung out to dry during lengthy drug addiction but is friends with above two. Looking for any way to get himself back outta the gutter. Is avoiding his old dealer (now lvl 1 contact) for whom he used to do jobs for.2. Next, I'll determine
what kind of job this is and what the target is.
Who wants the job done and who it will target.
Why they want this job done.
When they want it done (i.e. by next week, immediately, whenever), and finally,
where the target itself is.
So, we have a unique team here and an idea of what sort of things they may be good at and what the players themselves like.
Seeing how the players like gambling, I've determined that I want to include this somehow. The team looks like it could handle some low-intensity conflict at least, so we'll throw in some of that. We'll maybe want to throw in a magical threat of some sort for the mage, and probably a little infiltration or close combat for the "ninja". The third guy had a drug problem at one point, we'll try to work that in some how. I've determined that the job will come from the first guy's Yakuza contact. Looking at the team, I suspect that they don't need a ton of pay to maintain themselves. I will give them more than enough to cover rent plus leave extra as spending cash.
What I come up with is this:
The first guy's Yakuza contact will call him up and request a meet at a local restaurant. Over dinner, the yak offers them a job. The job is as follows: There is a mafia underboss who the yaks want eliminated. This guy is in charge of a club that offers gambling, drugs and prostitution in the Tacoma district. The yaks know that the guy spends a lot of time at the club (tell them what club/where it's at), but don't know when he will be there exactly. They want it done at the club, to make an example "that the Yakuza can get you anywhere". Pay is 20000 as a lump sum for the group to split.3. Determine what kind of information the team might want to find out before performing the job. Throw in
at least one good piece of information. If you want, throw in a little misinformation or red herrings as well. Don't overdo it on the red herrings otherwise the players won't make as much effort to find stuff out if they believe all they'll find is garbage. Remember that they may even decide to investigate the johnson, or whoever is giving them the job.
I have determined that if the team goes and checks the place out, they'll find a large club with a second story. If they have access inside and check things out, it'll be your average nightclub, but the second story is cutoff from the rest of the club and blocked by a troll bouncer that watches the stairs. If they try to gain access upstairs, they'll find that access is by invitation only. If the mage takes a look in astral space, he'll see an earth elemental that is watching to make sure nobody tries to sneak by astrally, or magically influence the bouncer to allow access.
If the characters ask around they'll get some info about what goes on upstairs. It will range from a VIP lounge, to a gambling hall, to the owner's apartment. In reality, it is all these things, offering sex, drugs, gambling, etc...
Sliding a good chunk of change the bartender's way [I]could get them access if they try that.
They may want to ask around on the street to find out additional information. A lot of this will be vague and at most times inaccurate. Asking around in the club (and with adequet bribes) will yield some information, possibly including that the underboss likes to come in on wednesday nights, that there is a combat mage that pulls security 5 nights a week, as well as other vague tidbits, possibly what kind of protection the boss has (which the bodyguard character should be able to size up appropriately if he sees them).[/I]
4. I'm running out of time, but that's the basics for that. You'll figure it out

Next, I'll throw in some complications. Don't go overboard on complications, but there should be some things the characters won't know, or that won't go according to plan.
As soon as things start going down, the team will run into an elemental, and most likely, the combat mage will be there when the boss is there. This will give the mundanes some trouble, but will really give the mage a chance to shine.
There may a good chance that things come down to hand to hand combat, esp. if the bouncer somehow becomes involved, perfect for the "ninja".
The other complication I'm going to throw in is that many of the upstair patrons are criminal types themselves. In essence, the team is going to run up against more security than they had previously thought, and may need to find an alternate exit. I will be sure to give them an option, probably through a window if they choose to take it, with a convenient dumpster below it.5. Last but not least. Keep notes of what happened and any actions the PC's may have done that would leave a loose end that you could pick up and use for future runs or complication (like and enemy showing up at a bad time). Always be ready to improvise, and accept that you won't be able to cover every possibility that the players may follow. Don't get too specific. Leave yourself room to improvise. I say this twice because it's important.
6. (optional) If you want, you can do what I do sometimes (and have fun doing), and just wing the whole thing. Improvise the whole run and let the chips fall where they do.
So that's it, I know my run example kinda sucks on a few levels and leaves a lot of important elements out, but I was really pressed for time. I hope this is able to help at least a little.