What is section targeting? Here is the official information on Adsense Help Center:
Section targeting allows you to suggest sections of your text and HTML content that you'd like Adsense to emphasize or downplay when matching ads to your site's content.
To implement section targeting, you'll need to add a set of special HTML comment tags to your code. These tags will mark the beginning and end of whichever section(s) you'd like to emphasize or de-emphasize for ad targeting.
The HTML tags to emphasize a page section take the following format:
<!-- google_ad_section_start -->
Page Content
<!-- google_ad_section_end -->
Now, how can you implement Adsense Section Targeting on New Blogger? I suggest you to use above the code before and after post titles and post content to get relevant ads. You should add the codes above before and after Post Title and Post Content tags.
Post Title <b:includable id='post' var='post'> <div class='post uncustomized-post-template'> <a expr:name='data:post.id'/> <b:if cond='data:post.title'> <h3 class='post-title'> <b:if cond='data:post.link'> <a expr:href='data:post.link'><!-- google_ad_section_start --><data:post.title/><!-- google_ad_section_end --></a> <b:else/> <b:if cond='data:post.url'> <a expr:href='data:post.url'><!-- google_ad_section_start --><data:post.title/><!-- google_ad_section_end --></a> <b:else/> <!-- google_ad_section_start --><data:post.title/><!-- google_ad_section_end --> </b:if> </b:if> </h3> </b:if> Post Content <div class='post-body'> <p><!-- google_ad_section_start --><data:post.body/><!-- google_ad_section_end --></p> <div style='clear: both;'/> <!-- clear for photos floats --> </div>