Always, always, always be doing something unless you're having leisure time. If you're at school/uni and have a free class, knock off some tute/home work. You'll find during your leisure times you will be more relaxed as you didn't waste time during the day. Same applies to work, get the work done and then slack off.
Set up templates in word, this saves heaps of time as you don't have to muck around every time you open a new document with the font etc.
Even though the topic is being efficient, do the best job you can with time permitting, everyone will respect you more. That being said don't waste time being over perfect.
Time is something you can never get back, just remember that when you dick around.