The gist of things: Jacob is looking to negotiate with a new supplier, but he doesn’t trust the group he’s in contact with. Maybe it’s just the weed- makes him paranoid- but there’s something shifty about them. He wants you to come and help with security. Saddle up and follow your GPS to the location he mentioned- he’ll get out and ask you to head around back with the car, in case you need to get out fast.
Turns out it won’t be you. After a little while Jacob will phone you- the dealers were phonies, they didn’t have any weed, and they tried to grab his “coil” (best guess? His roll of bills that was intended to pay for the weed). He’s got the front covered, and needs you to watch for them out back. Like clockwork, three dealers will appear and do a runner down the alley.
Though you can take them down from the car, it’s not advised- the alley takes a very sharp bend a ways down that will be hard to navigate, and you’ll shoot better with the on-foot auto-lock system. As it is, you’ll have to sprint to catch up with them, and it’s doubtful you’ll be able to take them all out before they reach the street outside. Gun them all down.
This may well draw the police down on you- if it does, you’ll have to lose your wanted level before going after the dealers’ boss. Either way, you need to pick up Jacob first, so get back to the car and get him from out front of the meeting point.
One note: if the cops do arrest you during the duration of this mission, it’s over, and you’ll have to retry it. This is a good general rule for most missions, by the way.
Once you’re in the clear (whether or not you got caught in the first place), Jacob and your GPS will direct you to a townhouse in Broker. Head there, park, and head up to the door. Take cover as recommended and Jacob will pop the door, revealing a gangman on the stairway. Take him apart.
Another gangster will open fire from the next room once the first falls. Jacob can’t get a shot on him, and recommends you drop him from the window while he’s preoccupied. This guy ALWAYS has a shotgun, meaning you get it when he dies, so what are you waiting for? Move behind cover to the window, lock onto the guy, and fire at him until he drops.
Jacob has a tendency to rush in at this point, but there’s still two other dealers in the house, and he isn’t indestructible, so you’ll need to rush in and help. There’s no good shots from the window, so head back to the door and wrap around to the living room/kitchen. Try and nab the shotgun- you may actually pick it up and not realize it- but stick to the pistol for this fight. The two remaining dealers will stick to their cover no matter what you do, so hit ‘em whenever they pop out to fire.
When they’re all dead, take the first-aid kit from the table and police the bodies for ammo. Once you’re done looting, head back out to the car. Jacob will ask you to take him to the Homebrew Café, just off the Alongquin-Dukes expressway across the island. Do so, and you’ll get your payment, completing the first Little Jacob mission.
Shortly after this (or possibly the second Jacob mission), Jake should phone you with the offer to hang out sometime. This is a very good thing, since Jacob (as mentioned) has arguably the most useful friend ability in the game. Be sure to take him up on the offer.
As to what he likes? I’m not sure. But the common knowledge is that the strip club is ALWAYS a good option. And if you’ve never been there, call him specifically about that- the start menu map wil helpfully mark its location in East Bohan for you so you can toss down a waypoint. It’s one of the more expensive options (potentially $50 for a proper disposition boost, plus $10 for two ways through the toll booth), but considering what you get, it’s well worth it (and also, it should never be a matter of complaint to attend a strip club). ---