Each individual is different and therefore must assess their own abilities accordingly. Making sure exercise remains frequent, intense and fun will help keep things interesting. Generally three to five days per week is considered a good rule of thumb to follow.
During exercise, intensity can come in various forms. Ideally for longer bouts of cardio training at a lower intensity is recommended. As a guide if you can have a conversation then you’re within this range. A more efficient method of training is at a higher intensity for shorter bouts. Exercises can range from rowing, cycling, running, swimming or anything else that increases your heart rate.
A few things to take into account when selecting activities are how they match up to your body’s current state. Upper cross, lower cross and pronation distortion syndrome are common imbalances that require avoiding certain types of activities until corrected.