Well, I haven't actually gotten my leader up to anything higher than 50 in my current game, but I have several gang members with 250 juice, 8 pistol skill, etc. I've lost a few of them in the process, and most of them have spent a fair bit of time in the hospital, so it's not foolproof, but it's not insanely difficult either.
I started my current game before the "jump in front of your leader" patch, and my primary goal was to keep my leader alive -- and squeaky-clean. This strategy relies on never committing a crime, and never letting anyone get arrested. It doesn't matter how many people die under your command -- if they never wind up in prison, you're safe.
Meanwhile, I've got a judge teaching law to my leader, so by the time I slip up and go to court, I can defend myself without trouble. Key things to avoid until then: I don't teach criminals; it makes me one. I don't let anyone under me do a non-interactive crime -- no selling brownies, no activism, no sweatshop workers. I never let anyone give up to the cops, no matter how good they are -- better to fight their way to martyrdom, even naked and unarmed, than to get arrested and risk a confession.
Recruiting is a very fast way to get to 50 juice points. Once you hit that, you have a +2 bonus to all stats. This is a waste of time for my gangsters, who can get to 50 almost before they're recruited, but it's a good way to give the leader a running start, and much safer than starting from 0.
If you're ready to begin murdering people, I hear the best place to get juice is the aptly-named Juice Bar -- there are lots of mostly-unarmed conservatives to hunt.
If you have a decent team of cop-killing thugs and want to take a run at something bigger, date someone from a building so you get a map of the whole facility. I dated a liberal judge, and got a full map of the courthouse. Once I had that, I could see where all the loot and action-points were, and could very efficiently run through the place grabbing anything that wasn't nailed down.
Eventually, the "MASSIVE CONSERVATIVE RESPONSE" (MCR) showed up -- which was great for me, because it meant I stopped having to battle security guards. I looted the entire place, slipped past the MCR (probably because they stepped onto my old square just as I stepped onto theirs!), and only had to shoot a single cop to escape at the end.
Yeah, I got lucky, but I wasn't risking my leader. With a skilled group of thugs, my leader should be very easy to keep safe -- I'll put myself at the top of the group so I always get the first attack, and then anyone I don't hurt/kill, they'll finish off. And if anyone actually hits me, any one of my team will be glad to take the bullet for me.
With the "jump in front" patch, it should be a lot easier to keep your leader safe, so long as you ensure your thugs have high heart and agility. To get their heart up (and wisdom down), always have them do both community service and activism before you recruit them.
If the patch had been in place when I started, I think I would've just gone out and tried pure thuggery -- and it's very likely I'd be the one with 250+ juice now, not my goon squad.