The answer depends on your lifestyle.  Are you an active person by nature?  Do you go out to play soccer every Friday afternoon like a good friend of mine?  Do you hike every Sunday morning?  Do you bike to work every day?  All of these things count as physical activity which you are trying to replicate when you work out.

In general, I would recommend that you get a serious resistance workout 3 to 4 times a week.  A resistance workout is something that challenges your muscles.  It could be rock climbing or it could be lifting weights, but it needs to really strain you to the point where your muscles ache and you feel tired, but not out of breath.

I would also recommend a good two or three sessions a week where you challenge your whole body and especially your cardiovascular system.  In other words, exercise which gets you out of breath.  This could be soccer, sprints, fast paced dancing, uphill hiking or anything else that gets your heart rate pumping.

Otherwise, just maintain an active lifestyle with plenty of walking and moving around.