Step 1 - Insert CSS in the HTML of your website
First you go to the Blog Title → Template → Edit HTML. Press Ctrl + F. You find <b: skin> ... </ b: skin> insert the following code in the middle of it. Or search]]> </ b: skin> and insert the following code above]]> </ b: skin>.
.avatar-author{float:left;margin-right:10px;border:0;border-radius:50%;padding:0;width:30px;height:30px}
Step 2 - Insert Javascript in the HTML of your website
Find </ head> and insert the following code before the </ head>.<script>
//<![CDATA[
function av(a){var b=a.entry.author[0];c=b.name.$t;d=b.gd$image.src.replace(/\/s[0-9]+(-*c*)\//,'/s30$1/');document.write('<img alt="'+c+'" class="avatar-author" src="'+d+'" title="'+c+'"/>')}
//]]>
</script>
Step 3 - Search <b: if cond = 'data: post.title'> then add given code above.
Note: You should note that there can be more than <b:if cond='data:post.title'>, so you should place this code just above the right code.
<script expr:src='"/feeds/posts/default/" + data:post.id + "?alt=json-in-script&amp;callback=av"'/>Now Click on Save Template button to save this template.You did successfully. Enjoy blogging.