Anything that increases your heart rate for extended periods will increase aerobic fitness. The best routines do multiple types of exercise - running, rowing, biking, sprinting, and speed walking.
There are equal benefits to doing one session a day or several short ones, so long as time is 30 minutes. You should do activities that raise your heart rate.
Ideally everybody should exercise for at least thirty minutes a day. This can include walking. Brisk walking is better. Higher intensity exercise such as running and cycling should be performed 3 times a week. If you are trying to lose weight make sure you undertake high intensity exercise 5 times a week. It should dramatically increase your fitness levels.
