Raise the stakes.
Best example: The Walking Dead
The Walking Dead's debut season was truncated for production and scheduling purposes, so the sophomore season was set to be the first real look at Frank Darabont and company's execution of an actual season of television. The result was a snail-paced, often stagnant arc, the last problem anyone expected a series set during a nihilistic zombie apocalypse would face.
Sure, one kid took a bullet while another one died, but those events were a whopping six episodes apart. In between next-to nothing happened, and everything felt way too...safe. When Dead returned from its mid-season break, it did so with a renewed energy, that took slow but certain steps to raising the stakes, and making us actually believe these people were living in, you know, the end of days.
The current third season has taken things a step further, upping the urgency, violence (it is a zombie show, after all) and most importantly nuance and character development, under the guidance of new showrunner Glen Mazzara, formerly of The Shield (arguably the master-class of urgency and suspense). Hell, they even made us kind of warm up to Carl, and feel for Lori. All of those pieces came together wonderfully in the series peak "Killer Within," and after this week's sure-to-be insane mid-season finale, Walking Dead will finally, officially be a series worthy of its monster ratings and buzz.