It depends on your clients in the class
Always do a dynamic warm up and ease into any High intensity cardio.
Mix things up! If you can do part of the class using a step or bosu along with squats and lunges you can incorporate all muscle groups along with cardio.
Have your class monitor their heart rates: ask them what they are, this way you will know if they need to be pushed or not
It would help if you could elaborate on your question a bit. What kind of cardio class? Usually you have a warm up, the basic core of the class, and a final cool down and stretch. The cardio sequence depends in the type of class.
Please give us more info on what you are looking for…