Start with small increments for both strength training, cardiovascular, and flexibility training. The most important thing to remember is to take the time to make it work. Do not rush it. If you push too hard too soon, you will get frustrated and feel exhausted. Getting plenty of rest is probably the single most important factor to recuperating from an illness.
Rest can include sleep as well as sitting and resting.
Getting enough sleep is important to the recovery process. Sleep is the time when your mind and body do a great deal of regeneration. Without sleep, your mental and physical processes suffer. It helps to go to bed at the same time every evening and get up at the same time every day. Even on your days off or days when you are not planning on doing anything, you will find that getting up, moving around some, and changing positions around your home will help speed the recuperation process.