DASHBOARD > DESIGN > EDIT HTML
to open template editor
Use keyboard shortcut ctrl+F to find <head> and immediately after that, add a single line
<base target='_blank' />so that it become
<head>
<base target='_blank' />
Save the edited template and viola, all links in your blog will now open in new tabs or windows.
Links:
1. Add Breadcrumbs in Blogger
2. Make Blogger blog comment dofollow
3. Related Post Widget for Blogger
4. HTML Parsing in for Blogger Post
5. Add three column footer to a blog
6. Post Summery on Blogger