Planning a routine, and getting a routine

Managed to go to the gym today and cardio with some intensity. I completed a 19 minute session on 60 resistance (which is 'average' when I am fit.) It was hard. I stopped almost entirely for 20 seconds during the last set, but was able to continue. I want to train with some sense. But without a certain intensity, and without a certain amount of exercise naturally behind me (3-4 weeks at least) I can't plan anything. Which makes this time of training strangely difficult.