Having a gym workout plan is a great way to keep yourself on track and motivated, especially if you work best with scheduling and organization. If instead you are a person who cannot stop freewheeling, it could be a beneficial way to add some order to your life. That said, many workouts can be performed equally well at home, with no equipment. However, if you do some basic planning, the gym gives you the chance to work each major muscle group in a variety of different ways.
The biggest reason to have a plan before you start your gym workout is that most gyms offer many different ways of achieving the same basic thing. Many floor exercises work the same muscles as equipment, many weight exercises work the same muscles as resistance bands, and so forth. Similarly with cardio, there are many options—cycling, treadmill, elliptical, and more. You also need to know just how much weight you want to use as resistance, how many reps/sets to do, and how long to stay on a given cardio machine.
Most non-bodybuilder gym plans prescribe 20 minutes of strength training 3 days per week. Each session should contain one exercise for each of the four major muscle groups: legs, abs, arms/chest, and back. Generally, you should do about 3 sets of 8 reps of each exercise. In addition, 20 to 30 minutes of cardio 3 to 4 days per week is recommended. The cardio and strength training may be performed the same day or not, as long as there is a day of rest between each strength training session.
The planning process becomes more complicated as you progress; you may find you really need to write out your plan or use a plan developed by someone else. (You can find many online, in books, or through a trainer.) It is critical to avoid over-exercising as a beginner; injury from overdoing it is one of the biggest reasons people do not sustain a workout regimen.
More advanced exercisers may use pyramid or reverse pyramid approaches as they perform sets. The pyramid is when you begin with a set of many reps with low weight, and then reduce reps and increase weight each successive set. The reverse pyramid is the exact opposite: start with more weight with fewer reps, then progress to more reps with less weight.i
Advanced exercisers will usually workout more days of the week. However, they still maintain at least one rest day between strength training sessions with a given muscle group. Usually, there is one day of no cardio—most people will take a rest from all exercise on this day. The amount of cardio time may go up to 40 minutes per day and be split between two different exercises on the same day (e.g. treadmill and elliptical).
The highly experienced may prefer fewer days with each muscle group so they can work a group extensively with a series of different exercises. However, this approach lends itself to building large muscles i and is therefore not applicable to people who just want the health benefits of exercise.
i Pena, Jimmy and Wuebben, Joe. (2017). “The Complete 4-Week Beginner’s Workout Program.” (Accessed 15 August 2017). http://www.muscleandfitness.com/workouts/workout-routines/complete-mf-beginners-training-guide-0.