Subscribers are those people who want to get notification if your website or blog has a new article or blog post. First thing you need to do to Double your website subscribers is to write quality contents that targets your specific niche. Secondly, you can put a little note after your website contents asking them that if they like the post that they just read, to subscribed to your blog. Another thing that you can is to offer free giveaways like ebook if they subscribe. Offering something is a good incentive for subscribing.

Hope that helps. Please dont hessitate to comment below if you have other successful ideas on how to double or triple your website or blog subscribers.