In David Allen's Getting Things Done, there's one tip I consider very useful but seldom practiced by many people:
If it takes less than two minutes to get a task done, just do it NOW!
Why? Because if you have to do the task anyways, it usually takes you more than two minutes to keep a record of it or delegate it to someone else. Of course, "two minutes" is just an idea. You can make it a "one minute", "three minute" or "five minute" rule. As long as you know that it's not "one hour" then it's fine.
"I don't need to keep a record of it; I'll remember to do it after I get the current task done." you say.
Are you sure you will remember? I don't think so. Even if you can remember, it means that that little task is sitting somewhere in your brain and thus preventing you from being fully concentrated on the current task. So, whether you remember or not it isn't good for you.
That's the reason I don't understand why it's so difficult for many people to reply to an email. I'd say that 90% of emails take less than two minutes to reply (assuming you have a decent typing speed). Yes, most applications like Gmail makes it so easy to reply to an email. Instead of replying right away, however, people choose to do something else and keep the sender waiting for an answer.
Be more productive guys!
Related post: Getting Things Done with GTDInbox