Everyone has a natural rhythm of energy to their day.  For example, for many people there is a bit of a lull after lunch where a nap seems more feasible than work.  There are also periods of time where you suddenly seem to be able to accomplish twice as much as usual.  This period of high productivity tends to last for about three hours, and will occur at a predictable time each day.  I call this period your "Highly Productive 3", or HP3 if you like acronyms. Although there are general trends of when people are most or least productive (like the post lunch sleepiness), only you can determine when you are at your most productive.  
 
Once you recognize when your HP3 occurs, you can plan to do the tasks that require the most focus during this time.  You will find that you get much further on these tasks than if you try to do them during a naturally low productive time.  Do your organizational tasks such as e-mails or phone calls during periods of lower productivity.  Protect your productive time by scheduling yourself into your planner, moving other appointments if possible to before or after.  Move your lunch or coffee breaks so that you can use as much as possible of your 3 hours on focused or creative tasks.  My highly productive time is from 10:30-1:30, so I eat a large second breakfast at 10:00, then lunch at 1:30.  Working with your natural rythm of productivity rather than against it will help you feel more accomplished at the end of the day.