Group rides will provide both the harder training required, and also help with "speed skills" like an increased cadence. Riding fast in a group is much easier, and that helps you get the skills. The fact that they will probably push your limits significantly will give you the strength. You will also see how they are doing it, and get ideas for good solo rides. Initially, you will likely not be able to keep up. Just smile through that period and work until you can not only keep up, but lead the group.
That said, your focus should be less on speed right now, and more on cadence (target 90+), smooth pedaling, position (work to gain the strength to ride the drops a lot), and general riding skills. Focus on those, and the speed will appear almost like a side benefit.