To keep up with client relations put reminders in your outlook (or any) calendar.
Calendars are commitment helpers -- they keep you honest. When you get an email or request that is date specific just drag it onto your calendar and set a timed reminder to get it done. To do lists are fine -- but attach a due date or just specify "appointment" with yourself to get what you need to get done. Get in the habit and you'll never miss an to do again.