Cardio Timing. Best to keep cardio and weight training separate as your schedule allows. For example, cardio early morning, weights after lunch.
Length of Cardio Session. Start with 20min, ramp up to 45min per session as you get into better shape.
Type of Cardio. Many athletes will use steady-state machines such as treadmill, elliptical, stair-climbers, swimming, etc. Sports such as tennis or basketball also are good forms of cardio. Most athletes will use a combination of cardio types.