1. Open the Layout panel and go to Edit HTML
2. Save your template by clicking on the Download full template button (to backup if something goes wrong)
3. Find the following code:
<b:include data='blog' name='all-head-content'/>
4. Add this code after the above code:
<b:if cond='data:blog.url == "http://blogs-tricks.blogspot.com/2009/08/how-to-write-or-post-scriptcode-into.html"'>
<meta name='DESCRIPTION' content='TipForBlogger: Blogging Tip And Trick, blogging site that provide information and tips to bloggers,SEO optimization,Free Blogspot Template And Site Info.'/></b:if>
5. Change the
red marked url with the full url of your post.
6. Change the green marked text with the description of your post
7. Create a code like this for each post.
8. Save your template.
NOTE: Don`t use more than 150 characters in your description.
Add the code for a post and put the code for the next post directly after it. To add description to the main page change the red marked url with the homepage of your blog: e.g: http://blogs-tricks.blogspot.com/