Planing, planing, planing!
Try to plan in advance how you want to structure you day. A pretty easy rule is the 60/40-rule:
60% of your day/working hours you are free to plan for your work.
40% should be reserved for unforeseen interruptions - because you'll be confronted with interruption if you like it or not.
If you come to the conclusion that your time isn't sufficient to get through your projects/work you should neither jump into multi-tasking nor reduce you buffer time for unforeseen events.
Both are fatal and will only force you into uncontrolled actionism.
You'll have to prioritize your tasks instead! How that is done you'll see in my next blog entry. Until then: Start planning!