How Hard (Intensity)
How hard you work out should reflect your training and fitness goals, such as whether you want to optimize your performance, just burn some calories, or get fitter. To really improve your aerobic or muscular fitness, you’ll need to do exercise of either moderate or vigorous intensity, not just easy activities. Be aware that higher intensity exercise (like interval training) may raise your blood glucose, though.
How Often (Frequency)
Being active every day is generally better for blood glucose. For aerobic exercise, the effects of the activity only last 2 to 72 hours, so your insulin action usually decreases if you go more than two days without motion. It's best to aim to do something daily (although the activity can vary), but every other day as a minimum. Shorter, but more frequent, bouts during each day also work well and can be more doable.
How Long (Duration)
The harder you do an activity, generally the shorter the duration you can maintain (and vice versa). While 30 minutes of moderate-intensity work or 20 minutes of vigorous-intensity are recommended most days of the week, keep in mind that doing most activities for longer will lower blood glucose levels more. Doing really long durations will also have effects that last afterwards, as long as a day or two.
What Type (Mode)
What type of activity you do is really up to you because almost any motion can benefit your health. It never hurts to pick activities that help you gain or maintain your muscle mass, however. Muscles are the main place we have to store excess carbs we eat, and the bigger the muscle "tank,” the more carbs we can store there (which helps keeps blood glucose levels down). Aim for getting more muscle then!