How do I manage time?

A friend of mine recently asked me what my secret to managing time was. Here's what I replied:

In general, there's always more work to do than I could possibly do. So, it's about deciding what's the most important thing that I want to spend my time on.

I usually spend a few minutes in the morning to write down my priorities for the day on a piece of paper, which I carry with me throughout the day. Every now and then, I take a couple of minutes to review this list or tick things off. Whenever I'm spending more than a couple of minutes on something, I check the list to see if the task I'm working on is actually the most important thing I should be working on. If it's not, I either stop immediately or take a minute to re-prioritise. That way, I'm always fully aware that I'm spending my time on what I decided was most important.

I very rarely feel that I'm not having enough time. Maybe the reason for this is because I'm continuously aware of what my priorities are.