A new feature in Gmail labs tab …
If you’re sick of typing out the same reply every time someone emails you with a common question, now you can compose your reply once and save the message text with the “Canned responses” button. Later, you can open that same message and send it again and again.
2. Click the Labs tab, find Canned Responses, click the Enable radio button to enable Canned Responses, scroll down and click Save Changes.
3. Compose an email message you’d like to use over and over again, and then click the arrow in the lower right-hand corner of the message window. Choose Canned Responses, and under the Save heading, select New Canned Response. Give your response a name and click OK.
4. The next time someone emails you something that warrants the canned response you created, reply to the message and instead of typing your response, click the arrow button in the lower right-hand corner, select Canned Responses, and then under Insert, choose the canned response you created in the previous step. You’ll then see your response appear in the body of your reply.
5. You can also automate canned responses to be sent out based on certain criteria (sender, keyword, label, subject and things like that).Click to read the article on google blog
Read more: Gmail Trick: Pre-Write Email with Canned Responses | TIME.com