You should ask your doctor about the post-surgery routine at your hospital. There may be a patient education booklet that outlines what will be happening but there are some general things for which you can prepare.
There will be pain afterwards, as with most surgeries. Be sure to discuss with your doctor and, importantly, the nurses about how often you can take your pain medication. It is not in your best interest to try to be stoic and not take the pain medication if you need it. If the pain is bad, you will likely not move your leg enough to be able to recover quickly.
Because of the general anesthetic, you will be asked to do deep breathing and coughing; this is to make sure your lungs are clear. YOu may also be taking medications to thin your blood to prevent clots. As your doctor or nurses to explain to you about the particular drug you are taking.
If you are prescribed support hose or compression boots, be sure to use them as instructed as they will help decrease the chances of developing a blood clot. You will likely be encouraged to do gentle leg exercises and you may have a machine called a continuous passive motion (CPM) machine. Finally, you will likely be seen by a physiotherapist who will teach you how to get in and out of bed and walk safely, as well as provide you with some specific exercises to help you regain movement in your knee.