Look at my blogposts bottom. I have add a "Related posts" gadget there. I think it is the smartest related posts gadget I have ever seen. Just copy and paste the codes below in a HTML gadget and you've done. You don't need to adjust the html gadgets space. It mas stay anywhere in your blog. But related posts must show on the bottom on every posts.
Thats all. You have done.
This smartest related posts gadget was made by More Tech Tips.