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Your best bet is to find exercises you enjoy, because you're more likely to stick with it. As long as your workout is challenging for you, that's what matters most. In general, I'd recommend 20-30 minutes of cardio exercise 3-4 times per week, as well as strength training twice a week.
You might ask your gym if they offer a free equipment orientation for new members. Lots of times you can get set up on a basic program to get you started.
Hope that helps,
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford
"No matter how slow you go, you are still lapping everybody on the couch."