In principle it is necessary to set a specific goal according to what you want to achieve. So if the person wants to lose weight will have to choose aerobic activities, if you want to gain muscle mass will have to work with weights, etc.
Also, it is always required to make a good warm up before you start, stay hydrated and stretch at the end.
Moreover, it is advisable to respect the proper rest between sets and not spend more than 90 minutes training.
If you want to build muscle you should not start with a lot of weight when you first are retaking the pace.
It is important to breathe properly, vary the activities to not be boring, not to abuse energy drinks and in all cases be supervised by a teacher.