Keeping the lens of focus shifting in more open games can be hard. Lately I've found myself doing this method, and so far it's working out pretty well. The idea is simple enough that I think it's good, but it also helps keep the spotlight moving from session to session and makes sure everyone gets their chance to shine.
2 Players In Focus
Going into a session I try to decide which two PCs I'm going to give focus to. This doesn't mean they're the be all/end all for the session, but it does mean that they get the majority of my prep time. If I try to have 2-3 ideas for every PC, I try to have 5-6 for the Primary PCs. That way if one thing doesn't pan out, I have more ideas for them. I have things prepared to go back to them more often.
As for the other players, they still get prep, but not as much. Like I said, I aim for about 2-3 things for them. Now a "thing" could be as small as "the blacksmith finishes the sword that Dunric ordered" or as complex as "The Lordling PC is invited to lunch with his mother, only to find several political rivals are already there." It's just stuff that moves that character along either in the meta plot or their personal plots they have going on.
What If the PCs Don't Cooperate
What if the PCs don't cooperate with going through my list of stuff? Well, that's just great then isn't it? I mean, if the PCs have their own agendas, then I can go through with that, however, I plan assuming they don't. And I plan assuming that they may linger on things I don't expect, or will come up with ideas in the middle of things.
That means that some of what I have prepped may spoil. It may become unavailable if the PC doesn't get to it in time, or isn't available when it comes up. Other things might come looking for the PC, only worse than they would have been if the PC had been there when I needed it. Finally, other things will wait - or even improve while left on its own.
Room To Maneuver
It's important to leave room to maneuver. PCs are clever and do their own thing. Ideas run rampant and snowball. Dunric's sword, and collecting it, could take a whole session if the right things happen in the right order - often starting when Dunric decides he doesn't want to pay for the sword afterall, or wants to steal something to go with it.
Because of this, don't expect to get through your whole list. Some items will hold over for future sessions. Others will just go away. It doesn't matter, as long as you have them for the session.
Try To Keep The Focus On The Primary
The goal is to keep the spot light on the primary characters more than on the secondary over the whole session. Again, this doesn't mean other PCs play second fiddle, it just means that there is a bit more stuff for the primary. This may get broken, but the idea doesn't work if you aren't willing to shift which PC gets focus from session to session.