I have broad strokes in mind, but I wing it on the details. That said, my games tend to be pretty combat heavy. Not brainless D&D "kick in the door" stuff, mind you, but with a fair number of fight scenes, and with chances for each character to shine (regardless of their favorite type of combat), whenever I can fit them in -- maybe the Yakuza boss is an arrogant martial artist so the close-combat guy will get a chance, maybe the Humanis Policlub guys have a decent shot with a bolt-action set up on some high ground so the team sniper can look cool, maybe the gang boss is a badass Combat Mage that's just itching to spell-duel, mano y mano...
I'm not afraid to reward folks who make brave/awesome choices, but I'm not afraid to kill folks who make stupid ones (and there's a fine line there). I like plans and ambushes as much as the next guy, and sound tactics will be rewarded by an appropriately high body count. Kamikaze charges are likely to BE kamikaze, though, because I let the dice fall where they may.
My one hallmark GM move? If characters get too bogged down in obsessive planning -- so much so that they're really breaking the pace of the game, overthinking things, and making it work instead of fun, folks are losing interest, or whatever? -- I throw a team of commandos at them.
COMMANDO ATTACK hasn't failed me so far.
Invariably, there's someone they've crossed -- maybe that adventure, maybe that plot hook, but maybe something older coming back to haunt them -- that has the resources to send some second-rate merc types after 'em. Sometimes the commandos are obviously tied to a given corporate entity, or a payment trace links them to a bad guy, or whatever (so that they're a plot device delivery system). Sometimes the commandos are just there to wake them up and sling some dice, get the blood pumping, and get them eager for payback. Invariably, the group gets a few cheapie SMGs or a shotgun or two out of it, some urban camo, maybe a few extra grenades (yet more prompting for them to go 'grrr' at the bad guy)...
I always run them as kind of second tier baddies, don't use cover and concentrate fire so much, don't handle them as smoothly and tactically as I would a "real" encounter (don't use and abuse Combat Pool, in previous editions, the way I could)...it's just a little nudge, a little danger, a few boxes of damage here or there (ideally, in SR1-3, a few Light and Moderate wounds all over the place).
COMMANDO ATTACK. The answer to the Shadowrunners-overthinking-it problem.