Keep them short and to the point. Nobody has time to read long emails. When I get an email which has a lot of questions then I put them aside thinking that I will get to them soon but that soon never happens.
Some famous quotes on this subject
The most valuable of all talents is that of never using two words when one will do. ~Thomas Jefferson
If it takes a lot of words to say what you have in mind, give it more thought. ~Dennis Roth
“Brevity is the soul of wit” - Shakespeare (Hamlet)
Need someone to respond to your email? Do not ask too many questions in the email. Make it easy for them to respond.