Pick a day with great weather and a route that looks enjoyable and go for it! You already do 30 miles, whats another 20?

Before getting my new bike, I hadn't been on one in years and had never been on a road bike. My first time out I did 20 miles. The next week I did 40 miles, then 60. Admittedly I started out in really good shape because I'm a runner, so no way I could have hopped on the bike and done 60 miles that soon otherwise. I still paid for it though as cycling works your muscles in a different way than running, but it was still a great ride! Some people prefer to stay around 40-50 miles solo because it can be difficult without having someone to draft at times when pedaling into a head wind, but otherwise I enjoy riding long distances solo. It's good, quiet, alone time. If you get out in the country, you feel as if its only you, the road, and nature. Really a peaceful and rewarding experience.