Write the past. An interesting idea put forth in Discovering The Writer Within, Interested me because sometimes I use it unconsciously and sometimes consciously. When working on a story or just trying to prime the pump I often look to the past. Part of my past is remembered things. These remembered events and impressions can add a lot to a story. What parts of these remembrances does one need to recall.
First are the senses and memories of them can conjure ways to add depth to a story. Sight, sound, touch, taste and smell. To these add your own reactions to an event. We've all been afraid. We've all had the first kiss and many other first. Some times things occur again and again. When working on a scene with your characters remember those times when a similar act happened in your life. Doesn't mean you have to write this step by step but if that's what it takes to get it down on paper go with the flow. Much of what you free write to add your memories to the incident you're writing will be taken out but there will be passages that give you that "Oh Yes" feeling.
During this session of memory don't think about your story just go with the impressions of what happened to you during that time. I've often used a memory to evoke what I was feeling and put it into a scene. So when you're having a rough time with an event in your characters' lives, draw on your own memories and sit dow and just write what you recall. Don't stop to worry about the words you've chosen or the punctuation and grammar. Once you revise these words is the time to do that.