1.Login to your blogger dashboard--> layout- -> Edit HTML
2.Click on "Expand Widget Templates"
3.Scroll down to where you see below code:
4.Now Copy your Mixx it Button code and paste it just below the above code.
NOTE: If you can't find <div class='post-header-line-1'/> in your template paste your Mixx it Button code just before <data:post.body/> .
<div style='float:right; margin-left:10px;'> <img align='absmiddle' alt='Add to Mixx!' border='0' src='http://www.mixx.com/images/buttons/mixx-button4.png' style='margin-left:20px;'/> <a expr:href='"http://www.mixx.com/submit?page_url=" + data:post.url'> Mixx it! </a> </div>