The tweak will enable the display of thumbnails automatically generated from images used in your posts on your homepage, while the full-sized images display on post pages.
Post Thumbnails will make your blog look fine if you are using the Blogger Jump break feature to add "read more.." option to your blog posts. Below is a screenshot of a post excerpt on my blog with a post thumbnail aligned to the right and also with a "read more" icon.
How To Add Post Thumbnails To Blogger Homepage
==> Log in to www.blogger.com
==> Back up your blog template
==> Go to "Template" > "Customize" > "Advanced" > "Add CSS"
==> Copy and paste the code below in the css window:
border: 1px solid #eeeeee;
-moz-box-shadow: 1px 1px 5px rgba(0, 0, 0, .1);
-webkit-box-shadow: 1px 1px 5px rgba(0, 0, 0, .1);
box-shadow: 1px 1px 5px rgba(0, 0, 0, .1);
==> Click "Apply to Blog"
==> Click "Back to Blogger"
==> Go to "Template" > "Edit HTML"
==> Click inside the HTML editor
==> Use CTRL F to find the second <data:post.body/> in your blog's HTML
==> Copy the code below, directly above the second <data:post.body/>
<b:if cond='data:blog.pageType == "index"'>
<img class="postthumb" expr:src ="data:post.thumbnailUrl" expr:alt="data:post.title"/>
==> Save your template
==> View the homepage of your blog and you should see the post thumbnails appearing on each post excerpt.
NOTE: There must be an image in your post and you must have added the read more option to your post.
I hope it works for you.