Tasks to take on at the end of filling up a paper notebook.
Read through the whole thing, copying out the good parts. There are bound to be enough good parts that you want to save and remember some of them, and scanning them in is one way to preserve the rough qualities. Retyping a clean copy with additional notes inspired by the original is another way to manage that same task.
Consider shredding the bad parts. Forgetting is as important as remembering, and you can channel 15 minutes of Discardia by getting rid of junk that is just taking up space. Of course this is a horror if it's a true laboratory notebook, but I'm not going to make that assumption.
Compile an index of names. Figuring out who you were thinking of along the way is at least as interesting to methodically review as what you were thinking about, since the review process may be as simple as reconnecting with someone who sparked a great idea but with whom you haven't had that conversation.
Identify a suitable visual design for a new notebook. Figure out how to be inspired by the blank page again, and use a design that matches something that causes you to start the page full of ideas. A blank page can be more constraining than one that has some structure already filled in, and a great page layout can be inspiring.
Figure out what it is that you will be carrying with you every day. The only way to fill a notebook is to have it handy. Don't allow it to go unused simply because it isn't there, or because you don't have a pen or pencil always within reach.
The original of this was 5 short lines, and it got longer in the process of writing for the net. It also made me want to discard things in order to leave room for more conversation.