How do I stop the generic thoughts from overtaking the original ones?

I'm having an issue with not writers block per say but in a way it is. I'm trying to a novel but every time I try to draw out the plot I think of something far too familiar. I have some things that don't sound like everything else but it's hard to find in them in the mess I call my brain. How am I supposed to find these thoughts and refrain from using the over-used m marketed ideas as much as is physically possible?