How to train a cat to move...

So, I have this cat. I suspect, out of all four of them she's the intelligent one. I catch her watching every little move I make and she's always the one who has to explore new bags and boxes. She knows how to open the door and I'm pretty sure she enjoys watching the weather channel. She's also dedicated. Entirely too much so. She has a terrible habit of purposely getting underfoot on the stairs. I live in one of those old style houses typical in the US north east with stairs we call widow makers because they're tall and the way they turn makes them easy to slip off of. This needs to stop. I'm going to end up accidentally stepping on her or falling and she simply doesn't respond to commands or being nudged out of the way. Can anyone offer any advice on what to do?