When I get stumped for ideas, I try to use the "Yes, and ..." method.
Listen to what your players are talking about IC. Are they pondering clues and mysteries you've already put in place? Is there an NPC they found memorable/interesting?
Take what the players are saying and then say "Yes, and ..."
For example:
PC1: Boy that old man we met in town sure was cranky, wasn't he?"
I think to myself, "YES, he was cranky, AND it's because he misses his long lost wife, AND he would love to find some memento of her."
From there it's a short jump to a "Black Jay" style plot hook ala Village of Hommlet.
Basically, just listen to the players, and then carry things to their logical/illogical conclusion.
PC2: Wow, those kobolds we fought sure were tough!"
I think to myself, "YES, AND, they are so tough, they are actually planning to invade town AND carry off some slaves. AND they'll prbably attack tonight while the PC's are resting."
There are doubtless a ton of smaller adventure hooks already in place in your campaign. With a little "Yes, and ..." they can become useful plotlines, and help end your writer's block.