The fourth factor for success is exercise choice, which I touched upon in the third factor.
While there are no bad exercises per se, there are some exercises that are far more effective than others. There are also some exercises that are inappropriate for certain people, either due to previous or current injuries, complexity or limitations in mobility.
In terms of what exercises are the most effective, then these are undoubtedly multi-joint (or compound) exercises. While there is a place for single joint (or isolation) exercises that focus on the arms, or other smaller muscle groups, these should be considered secondary and of less importance to multi-joint exercises.
The most important multi-joint exercises include all forms of squats, all forms of deadlifts, big presses (like military or bench) and big pulling exercises (like pull-ups, pulldowns and all forms of rows). These should form the basis of your programme most of the time and be focused on first in your sessions, with the single joint exercises added in as assistance exercises to ensure you are covering all the major muscles in the body.
That final point is a major issue for most gym goers, they just never stimulate enough of the body’s muscle mass to make a significant difference. So guys tend to focus too much on the mirror muscles (pecs and biceps, they’re easy to spot at the gym) and women focus too much on the “core” muscles and less challenging exercises.
I know I keep banging on about it, but your body won’t change unless you force it to, and it certainly won’t change if you keep only working parts of it. The muscles on the back of your body I would argue are actually more important than those on the front and legs just as, if not more important than, your upper body.
I understand that the big exercises scare people who think they look like hard work, but that is precisely what makes them so effective, because they have the biggest effect on your nervous system and muscles.
If you really want to change your physique for the better then you have to choose the exercises that will have the most impact, and ensure you work your whole body on a regular basis.