Double the Value of the Email You Send
Here's an easy way to double your email value: Wait 5 minutes before sending.
That's enough time to come up with one more idea that you could include in your original email. Time enough to fix a typo. And time enough to see if someone else has already responded to the same question (in cases of multiple cc'd emails).
How does this double your efficiency? By making the emails people receive from you twice as valuable. If you could cut the number of emails you sent in half, but make the ones you do send more valuable, the people who receive email from you will find your emails twice as valuable.
Also, within that 5-minute time window, think to yourself, "Will everyone receiving this email find it valuable?" If not, remove people from the cc field or don't send the email at all.
Respecting your reader's time makes your email (and you) more valuable.