When we get stuck for a while we have a couple of tricks we try.
First, we step away for a day of what we call filling the well. Writing, like other creative endeavors, takes a great deal of both physical and emotional stamina. Often, when we are staring at the blinking cursor and nothing is springing to the page, we are simply exhausted and need a day to recharge. We spend a day reading, watching television or movies, listening to music, playing a video game - anything that both relaxes us and reawakens our own creativity.
If, after a day of refilling our creative well the words will still not flow, then we take a look at the detailed outline for the scene that we are struggling with. We do additional pre-writing, make sure that the scene still works at this point in the plot, and sometimes even act out what needs to happen.