Adding Google adsense ad in post body is a great way to increase CTR . But adding adsense code inside blogger post is not straight forward. Following is the procedure for doing this.

Login to your Adsense account , select and copy(Ctrl + c) the adsense code that you want to use.
Follow this link to go to Adsense parser - which will readily convert your adsense code to new Blogger compatible code. Copy this new code(Ctrl +c)
Login in to Blogger Dashboard.

Select "Layout" link for the blog in which you want to add adsense code.

Click on "Edit HTML" link.
(p)(data:post.body/)(/p)

check "Expand Widget Templates" check box.

Search for following in template.

Paste the code selected in step 2 under or above following tag(depending on where you want the add)