gỗ ghép
Chèn đoạn code sau bên dưới </b:skin> :

<!--them bai viet lien quan-->
<b:if cond='data:blog.pageType == &quot;item&quot;'>
<script type='text/javascript'>
//<![CDATA[
var titles=new Array();var titlesNum=0;var urls=new Array();var time=new Array();function related_results_labels(c){for(var b=0;b<c.feed.entry.length;b++){var d=c.feed.entry[b];titles[titlesNum]=d.title.$t;for(var a=0;a<d.link.length;a++){if(d.link[a].rel=="alternate"){urls[titlesNum]=d.link[a].href;time[titlesNum]=d.published.$t;titlesNum++;break}}}}function removeRelatedDuplicates(){var b=new Array(0);var c=new Array(0);e=new Array(0);for(var a=0;a<urls.length;a++){if(!contains(b,urls[a])){b.length+=1;b[b.length-1]=urls[a];c.length+=1;c[c.length-1]=titles[a];e.length+=1;e[e.length-1]=time[a]}}titles=c;urls=b;time=e}function contains(b,d){for(var c=0;c<b.length;c++){if(b[c]==d){return true}}return false}function printRelatedLabels(a){var y=a.indexOf('?m=0');if(y!=-1){a=a.replace(/\?m=0/g,'')}for(var b=0;b<urls.length;b++){if(urls[b]==a){urls.splice(b,1);titles.splice(b,1);time.splice(b,1)}}var c=Math.floor((titles.length-1)*Math.random());var b=0;document.write("<ul>");if(titles.length==0){document.write("<li>Không có bài viết liên quan</li>")}else{while(b<titles.length&&b<20&&b<maxresults){if(y!=-1){urls[c]=urls[c]+'?m=0'}document.write('<li><a href="'+urls[c]+'" title="'+time[c].substring(8,10)+"/"+time[c].substring(5,7)+"/"+time[c].substring(0,4)+'">'+titles[c]+"</a></li>");if(c<titles.length-1){c++}else{c=0}b++}}document.write("</ul>");urls.splice(0,urls.length);titles.splice(0,titles.length)};
//]]>
</script>
</b:if>
<!--ket thuc-->

Tiếp tục chèn đoạn code sau vào vị trí cần hiển thị bài viết liên quan  : 

<!--chen bai viet lien quan-->
<b:if cond='data:blog.pageType == &quot;item&quot;'>
<div id='related-posts'>
<b>Bài viết liên quan:</b>
<b:loop values='data:post.labels' var='label'>
<script expr:src='&quot;/feeds/posts/default/-/&quot; + data:label.name + &quot;?alt=json-in-script&amp;callback=related_results_labels&quot;' type='text/javascript'/>
</b:loop>
<script type='text/javascript'>var maxresults=5;removeRelatedDuplicates();printRelatedLabels(&#39;<data:post.url/>&#39;);</script>
</div>
</b:if>
<!--ket thuc-->

Tham khảo thêm cách làm khác :

https://gicovietnam.blogspot.com/2017/06/code-tao-bai-viet-lien-quan-cho-blogsot.html
http://www.terocket.com/2011/07/tien-ich-bai-viet-lien-quan-cho-blogger.html
https://freewebs.vn/hang-free/tao-cac-bai-viet-lien-quan-cu-va-moi-theo-chu-de-trong-blogger.html