I'm still just a 3 week old newbie - so, I'm in the stage of building habits and building trust in my system. I spend time every morning on Collection, Processing, Organizing, and Reviewing - which basically means ensuring that my Next Actions list is up to date before I start the workday. The rest of my day is DO, unless an emergency comes up that will cause me to reassess.
My Next Actions list is a spreadsheet with one row per active project, and room for one or two next actions, and blank rows at the bottom for Ad Hoc next actions (longer than two minutes but not multi-step). I'm trying to make my Next Actions small enough so that I can easily make progress, otherwise I will fall into the same old trap of getting overwhelmed and looking like this: Given the number of interruptions around here, that means anything longer than 15 minutes probably needs to be subdivided into smaller Actions if I'm to make any progress at all.
Once the list is built, I print it, and highlight my 5 most important Next Actions for the day. That, plus my calendar, tells me what my focus needs to be for the day, barring any emergencies. Most days I have so many distractions that I don't get much past those 5. But it's progress, it's helping, and I feel better for it. On days when I do make a lot of progress, I'll update, reprint, and reassess my "high 5" whenever I feel it would help.
Until I build the right habits and build trust with the system, I'll continue cycling through the entire workflow at least daily.