RSS has become one of the most common ways to subscribe to a site's content, which is why increasing your RSS subscribers should always be on your to-do list.
Make sure that the content you're writing is easy to scan. It seems just about everybody has a million things to do, and that more than likely contributes to the perceived need for scanning. Usually most people feel time pressure, whether it's real or not, and that compels them to do that. When you make your content easy to scan, people will find it easy to go through it and understand what you're trying to say. It's probably a good idea to think ahead and imagine what your page content will be like in an RSS feed reader. The time crunch never ends because even if they subscribe to your feed, there's a good chance they sub to others, and then they will choose which feeds to read. So once again it's still important that your content is easy to skim, scan, and understand. You never want to present a "black wall of text" to your readers because it will be overwhelming, and they won't read it.
Another strategy that works is giving people a nice gift in exchange for their subscription to your RSS. You can offer people something for free, and it has worked for email list marketing for many years. It certainly won't hurt anything to test this approach. You'll get the best results if you add value to your subscription by way of a decent valued gift. This is a sure shot way to get quality subscribers that are actually interested in getting updates from you.
You'll have the best results with your site and marketing if you ensure quality and unique content goes on your site. Avoid using any "me too" content so that your subscribers get unique information delivered to them. If you do use PLR content, then you may find that people won't respond to you if they've seen the same information on other sites. It's just that unique content is the best, if it's done well, and a feed with unique content is more valuable than a feed with PLR content.
The best approach to increasing RSS feed subscribers is to put out first class content and engage your readership community.