I walk, do a few exercises with stretch bands and hand weights, and ride. My riding starts out slowly in the spring and I add miles and hills in early May. I'm currently up to my 38 mile route which includes 15 miles of hills. I hope to be doing 20 miles of hills by summer's end. Then when the days get cooler (October-November) I back off on the hills and just do miles. I don't own a trainer so try to ride as much as possible through the winter.
This plan may get derailed next week when I see the sports med doc about my knee (see a few posts above for that story).