Notes are key. When you see a scene in your head, it's best to jot down a few notes to remember all the detail. That's what I did the past couple of days. I see a dramatic scene in my head for the sequel and I have a few pages of notes to refer to, to bring it back to life for me. As I review them, I see the whole scene very clearly once again. It's also a great way for me (or I think any writer) to get excited about writing and sit down to the computer to type out another great page, paragraph or chapter! :-)
Odd... You never know where inspiration to write will come from. I've been inspired by love, also by something that made me feel sad, or even a piece of music. When it comes, it's like a brick wall that hits you and you can't avoid it, and you must write what you see and/or hear. It's one of life's awesome little surprises. Recently, I was inspired by the sight of an unusual tree and a new chapter was born. :-)
As I was lying in bed last night wondering what would happen next in my sequel (I have about 11 chapters written so far) I had a few ideas about how to continue. For about 2 weeks, I wasn't sure what to write next or how to continue my storyline. It's funny... you can want to write, but if the ideas don't come, all you can do is wait. After jotting down a bunch of detailed notes about what I saw in my head, I am now ready to get back to the story. :-) Sometimes, things are worth waiting for - rather than forcing it.