Get, and stay in the habit of checking your appointment book and ToDo list every morning. It doesn't matter how well the HP Palmtop organizes your appointments, if you don't look to see what's coming, you'll miss it.
Occasionally I'll backslide on this. I'll be in the habit of checking APPT for months and then slip right out of the habit. When this starts happening, I set an alarm to play at the time I usually arrive at the office. The appointment says, "Check your appointments and ToDo's!" Once this didn't work, so I set five appointments for the same time, five days in a row. It was annoying, but I re-established the habit of checking APPT.
If I have a really important appointment coming up, or one that I have to prepare for, I set more than one appointment for it. For example, if I have to prepare a report for a meeting, I'll set an appointment for three days before the meeting stating, "Prepare report for 10/25 meeting." If I want to make sure I leave a meeting on time, I'll set an appointment for the time I want to leave. The alarm rings, I check my appointment book and say, "Sorry, I've got to go."