Cadence is going to vary from person-2-person, so don't put to much emphasis on it. Instead, try finding a pace, at a comfortable cadence, where you are starting to experience labored breathing but can still carry on a conversation - that's about where you want to be when riding longer distances and where you'll start experiencing some basic conditioning. Faster riding over shorter distances (such as interval workouts) would be another way to achieve conditioning, but use longer distance riding as a basic first step.