First you find this code <Variable name=”main.section.margin” in HTML section of your blog by ctrl+F method. I think you know this. If you have any problem then post your comment at the below of this post.
See the light blue color shaded portion . I have changed the value to 5px ( value=”5px”/>) from 15px. see the changes by clicking on preview tool .
The light green edit portion reduce the padding horizontally to the main post section of the blog. I changed it to 5px (=”5px”/>) from 15px.
See the yellow edit portion . It will do real miracle for reducing margin above the main body ie below the header. Many blogger are hungry to get the help to reduce gap below the header. I changed it to 15px(value=”15px”/>) from 30px.
These are the most important edit. Many blogger does not give you this trick. But I believe to give real value from my site. 100% genuine tricks. If you feel any problem then ask freely.