I keep a pile of blank checklists and use one for each project. I outline the actions (in order) on the project sheet, and on the (blank) back I keep any notes that I need to make. I then copy any Next Actions from that project list to my Next Actions list.
Most of my projects don't require more than one page of notes, but for the few that do, I either create a new GMail label named after the project (for electronic notes) or put paper notes right behind the project sheet.
Welcome to GTD! It's a great foundation that will serve you well.