To come up with a blog name try and think of names related to what your blog will be about.
Is it a tech blog, health blog, etc. Try to find a domain that has at least part of the name of what your blog is gonna be about.
But if a domain that would be related to what your blog is about is not available then you can use a domain that has nothing to do with the blog.
Maybe use your own name for the blog and domain name if a domain is available in your name. Yourname.com where your name would be your first and last name.