There’s some ways you can take in order for people to subscribe / follow your blog:
Add users to your blog
Add users to your blog as subscribers. To do it, you need to go to Users → Add New. Find out more.
Share your blog’s feed address
External visitors can follow your blog by subscribing its RSS Feed – it should be something like http://yourdomain.blog.com/feed.
Mozilla Firefox already has a built-in feed button people can use to subscribe to blogs/sites, but you can also add the Syndication widget to your blog’s sidebar or widgetized footer in Appearance → Widgets.
Promote email subscriptions
Other cool way to do it is place a form in your sidebar for email subscriptions.