Often things that end up wasting our time are because we're being reactive rather than proactive with our time.
We have a tendency to react to every phone call, email or interruption that comes along as it arrives, which results in a fragmented day.
Better to be proactive and decide how you want to spend your time rather than have others decide for you.
It's also about setting boundaries and expectations - both with yourself and with your clients. Are your clients really expecting an instantaneous response to an email or is that the expectation you've set for yourself. Emails are rarely that important and given the unreliablility of email systems or over-zealousness of spam filters it can take a few hours for an email to get through to it's destination. Yes, 90% of them arrive almost instantaneously but there's always those that don't. Set yourself a realistic timeframe in which to respond - whether to phone calls or emails.
Set a boundary around your time. If you're busy or need some uninterrupted time - allow calls to go through to voicemail and respond as soon as you can. If you frequently get interrupted by colleagues - learn to say 'no'. That classic question "Have you got a minute" - which a) has already distracted you and b) never really is a minute.
If you work in an office - close the door and tell staff and colleagues that if the door's closed you're not to be disturbed. You can even stick a "please do not disturb" sign on the door just to get the message across. If you work in an open plan office you can still try something similar - I used to put a sign up at my desk - the equivalent of the do not disturb sign.
Book a meeting room if you need some quiet time or work from home - you can get a lot more done. If you work from your own home office and still get bothered by interruptions - go elsewhere. Take a pile of paperwork, research material or your laptop to somewhere where you can't be tracked down or interrupted - hotels often have an area where you sit undisturbed for a few hours with a coffee.
Organise you day so that you can deal with emails, phone calls and meetings in chunks of time. Plan your own time into your diary in the same way you plan meetings.
If email or the internet is a big time waster for you - take a look at my articles on these two particular topics or send me an email and I can send them to you.