Ready to get fit? Ok. Wear your gym clothes (important that you wear comfortable clothes, especially those that are snug and stretchable along with a good pair of shoes) and hit up the gym with the following regimen.
Begin the workout with stretches for each body part. It is important that all body parts are supple to avoid injuries through stiffness or excessive gym pains. Start from the neck rotation and work down to each body part. Each stretch should be of 2 sets, 15 repetitions each at a slow, controlled pace. Throw in 2 sets of 10 repetitions each (known as reps) of pushups for a great upper body.
A good workout always starts with Cardiovascular Exercises (or Cardio for short). Cardio will help your body get more supple by warming up which will result in lesser injuries and gym pains and will increase the metabolic rate. Increased metabolic rate will burn fat faster during weight lift.
Start with 5 minutes of treadmill (which can be slowly scaled up as endurance increases). Do thirty seconds of walk (say at setting 3 of generic treadmills) and then 30 seconds of brisker walk (around setting 6 of generic treadmills). Remaining 4 minutes alternate with 1 minute of running (say setting 9 on generic treadmills) and 1 minute of brisk walk. Slow down the last 30 seconds to allow the body to calm down.
Some people prefer to run continuously instead of alternating run and brisk walk. However, as per scientific studies, the alternating run and brisk walk is more beneficial. Make sure you play around with the settings to see what is the best speed comfortable for you. Do not worry if your friends are on a higher setting, you will eventually get there. You can also increase the incline to make it harder. Be careful if you have knee related problems.
Complement the treadmill with a followup of 5 minute biking. A gym will usually have 2 kinds of bikes viz. Mountain Bikes (which have 2 type handles, straight and curl) and Sit down bikes. If Mountain Bike is comfortable, use that as it will work your abs also while you bend over it. If not, use the regular sit down cycle.
Alternatives for cardio include stepper, cross trainer (much easier on your knees than running) or just climbing the steps up and down.
Once you are done with the stretches and cardio, pick up any 2 variations of each body part (Shoulders, Biceps, Chest, Triceps, Back, Legs) from the exercise list and perform 2 sets of 10 reps each. Finish up with any 2 variations of abs exercise (preferably one working your lower and one your upper or side abs).
It is always recommended to lie down on the exercise mat or relax on a chair for a bit before you head out to allow the body to cool down.
If you just want to stay fit, 3-4 times a week is essential, 5 times is recommended. If you are serious about body building, warm your body for 2 weeks with this regimen and move to the Intermediate workout.
In short: