One of the things I change most often when doing blog design is evening up the date header with the post title. As seen in the image below you can see that there appears to be a tab on the post title but the date header is left justified. Here's how you can easily even them up.
Simple click on "edit HTML" from your design page, then scroll through all of the HTML code until see the section for "posts" (it will be right after "widgets" but before "footer". Once you're in that section of code then look for the portion of code seen in the image below.
Once you find this code simply change the number in the highlighted portion from
-15px to 0px. BEFORE saving click "preview" to make sure that you like what you see. If so, then simply click "save template" and you're done!