The first thing that I always try to do is back up!!
One day, you might make a mistake and your whole blog is gone
So try, at least once a week or once a month to back up.

There are two things you would need to back up to get your blog back.

Template (or theme)
Content (all your pages/posts)

To back up your blog --

Go to Blogger

Go to the account you created your blog with and
then on your Dashboard page -

Go to THEME

 

Then click on the dots - and choose Back up



Then save this file somewhere on your computer, where you can find and
restore your blog!

Now this will only back up the theme, to back up the content (all your pages, posts, etc)  go to my post -
CONTENT BACKUP