How do you get faster?

[aicabsolut]

Find some buddies to ride with who are a little bit faster and stronger than you are. Ride with them and stay with them. When you can do that consistently, break out the hurt stick and make them try and keep up with you.

This is possibly the most effective method, so long as you have the mental toughness to keep pushing yourself when your buddies are kicking your butt. It is much more effective than using tools (like a HRM) to try to push yourself outside your comfort zone. They are pushing you, and sometimes you can really do more than you think you can. Don't do this every ride, obviously. It will get demoralizing and you don't want to be pushing your limit ALL the time. If you have a good group that challenges you, is friendly and makes the ride fun, you'll certainly get faster learning how to keep up with them.