1. PUT SOME MEANINGFUL CONTENT INTO SUBJECT.
By far the easiest way to make your emails easier to find, understand and act on is to put the heart of the message into the message subject. This means that people will see it even when they are only looking at a list of pending messages. Let's suppose that a webinar has been scheduled, the subject "Webinar" would be almost useless. Much better to write "Networking webinar scheduled for 11 January". This simple trick means that people are much more likely to open your message and read it. In some cases they may not even need to open it. For example, if I send someone a link and they answer with a short mail with the subject "Thanks for the link" I don't need to open it. Months later if you need to look for an email these clear message subjects will also help you to find them faster.
2. KEEP YOUR MESSAGES SHORT. Long emails take much more time to read, they are less likely to be read and you are much less likely to get the response you expected. Writing a shorter email may take you a little more time but the overall time to get the reaction you would like will be much shorter. Write a first draft then go back and delete all the information you don't really need. Make sure also that the most important information is at the top and if you link to something summarize briefly what the link contains. Never attach a file unless you have to. When you are sending a photo you need to attach the photo file, but when you are sending a text beware of attaching a separate text file because people are much less likely to open it. Cut and paste the text content into the body of your message instead.
3. CONSIDER CHANNELS OTHER THAN EMAIL. Many emails are not actually necessary but they fill your intray and make your phone beep continually. Very often they can be replaced by some other form of communication. Consider instant messaging, social media pages, twitter, text messages, telephone, paper letter and even face to face contact. By moving some of your communication into other channels you can very often save time for people at both ends, but be careful to choose the appropriate tool for each person. Some people prefer text messages, some prefer voice mail and some prefer to communicate through Facebook or Google+. By choosing well you can sometimes get a quick answer from someone who might take a long time to respond to an email. I have met people who rarely get a chance to answer emails but can easily answer a text message; others can best be reached through Facebook.
There are many other ways you can use email more effectively, but with these three ideas you can already make a big difference and save the time you spend writing mails and waiting for responses. They work best when everyone uses them so share this note with your friends and colleagues so you benefit, too. Finally, note that there are some cultural differences in the way people use email so if you are writing to people from a different culture you should also read Email Across Borders -- Three and a Half Secrets of International Email.