The key to a good, productive day is the same as the key to a good workout. In a workout, the first set is paramount. If it feels good and you are able to push yourself - and respond, the whole workout will be exhilarating.
In business, the key is the first 15 minutes. If you can be productive in the first :15, then your day will fall into line. However, if you are distracted and move off course, then you are playing catch up the whole day.
Therefore, do whatever planning and preparation you need to both have a good first set and a good first :15. You will reap the rewards.