Let things burn

As much as you like your plans, as much as you come to love some of your NPCs, as much as the players will grow attached: protect no one and nothing.

Many GMs have a tendency, a very natural tendency, to coddle the PCs and to shield the NPCs that they care about. To preserve the status quo. To save their villains for a future confrontation, even when the PCs' moves and rolls and bold action should rightly put them in the ground.

That tendency? Burn it away. Then let everything else burn, too. You're not playing to preserve your darlings. You're playing to find out what happens.

This doesn't mean that you should go out of your way to destroy the things that the characters love. It does mean that you should threaten those things, and that if the characters fail to save them, you should follow through. Be okay with hard, irrevocable consequences. Play with fire. Let things burn.