Survivors will become your worst enemies here. Their AI pathfinding is mediocre at best, and often instead of attacking they'll just linger and let themselves die. However, you have no choice but to save them (well, most of them). So let me give you some advice to hopefully make your life easier. If you have been through the game several times already you probably have strategies that work for you, but here is what works for me.
If you can give a survivor a weapon, most of the time you should. If you have a big group, giving 2 or 3 of them a weapon is probably enough — they will fight while the others run. Sometimes giving a whole group a weapon is a bad idea because they'll end up killing each other.
What weapon you give them is also very important. Personally, I stay away from guns because with guns they have to stop and shoot, and this results in them being surrounded a lot. You'll also want to stay away from sharing your Mini Chainsaw because this just ups the speed at which they can kill each other, or often times you. They think they are helping get that zombie off your back, but instead they're taking a chunk of your life.
So, what should you give them? The 2x4 is one of my personal favorites, but really the Hunting Knife is probably the most useful. It can kill zombies in one hit, but only hits one zombie/friend/Frank at a time, so it can't do too much damage when everyone's around each other. Really, any melee weapon that only hits one enemy at a time will be helpful.
Whenever you can, use Waypoints over just having them follow. If you aren't using Waypoints by now, you've got some catching up to do. By holding the right trigger and pressing Y at a location on the ground, you will tell your followers to go to that point. They seem to get very determined when they have a destination like this and go straight there, trucking straight through anything in their path. Even the scared girls are pretty good about going here.
The real trick to this, though, is to tell them a point and stay just ahead of them, clearing zombies out of their way so they have a straight path. If you can master this you'll find that saving survivors becomes a whole lot easier than just telling them to follow you and turning around to see them stuck behind a plant.
Also, don't stray too far away. Get in the habit of setting a point semi-close, clearing out just ahead of it, and then setting another one in the space you cleared out. If you get too far away you'll cause the zombies you just cleared to respawn, and then not only will you have to kill them again, but all your survivors will be in the middle of this mess. Try and avoid this happening at all cost!
Any time you can, use this shortcut (opened by Greg, who is saved from Adam in "Out of Control"). This will make your life easier for 2 reasons. First off, it's a quick trip around half of the mall, and coming out of the bathroom in either area is fairly clear of zombies at all points in the game.
Secondly, zombies will not go in the bathrooms at any time unless you lead them in. So, if you need to save someone in Wonderland and already have 3 people with you, set your waypoint in the bathroom so they all stay put, go and save that person (who will then automatically start heading for the waypoint), cover them on the way back, and once there head over to Paradise Plaza or save. Trust me, it'll make your life easier!
Note that after any scenes where anything reloads, you'll need to reset your waypoint or else your wanderers will be running around trying to find you.
Often times you'll find that the most frustrating part of getting survivors back is getting them to go up by the air duct so they all make it into the security room. While I can't guarantee a way for you to get them all to jump up there successfully every time, I will say that this follows the rule of Waypoints being better than "Follow Me." If you set a waypoint just on top of it off to the left, most people will make it up there without standing in your way. If you have too many people at once then they'll all just kind of run into each other, but you can stand down on the bottom and kind of bounce them around a bit and run into them to get one to go up.
Maybe that's not much advice, but it's really a flaky system, so that's the best I can think to tell you.