I will always preach communication and intention.

You can have the best narrative, the most thought-out cast, the most detailed setting and lore and characters. 
It'll fall flat if you don't keep in touch with your players. People like to talk, people want to get to know their GM. If you're not engaged in the telling, then why should they be?
 
The hardest part of running a game, from my personal experience, is the intent of your setting and the plot. When do you drive it forward and when do you allow player influences? Too often will you intend for a linear story and it becomes lost to sandbox elements; suddenly you're stuck writing the same day and it drags on for far too long and now you ask - what else is there?

Players will be incredibly engaging in the beginning, they'll make the CS, they'll build relationships with other characters, and they'll hype it up endlessly.

Then they disappear. The first month is the most telling of who is in for the long haul and who is just there for the process of creating the character. Often all inspiration and thought goes into the CS and fizzles out too quickly. 

Have the [i]objective[/i] of your narrative already plotted out -- chapters, episodes, etc. It doesn't have to be written out from beginning to end, but I suggest having little blurbs or concepts written to yourself for reference. 

You don't need the fanciest interest check or ooc, but players like looking at aesthetically pleasing things. Details matter.