Since John Broz was mentioned, here goes:
he John Broz Method For Average Joes
John Broz says that the squat is actually an easy movement to train daily because it involves little local fatigue (unlike a bench press, for example). Start by squatting every workout. This doesn't need to be a maximum effort, but getting used to doing the movement is important. Keep repetitions low (one to five) and train even when sore from the previous session. It should be possible to work up to squatting every day in a relatively short time.
Once an athlete becomes used to squatting daily, each session should look something like this.
* squat, working up to a daily max
* squat, six to 50 repetitions of doubles and triples working back up beyond the daily max if the weight starts to feel light
* assistance or bodybuilding work, but only if time and energy permit
The John Broz system is certainly controversial and goes against many things held to be true. However, it is also certain that most trainers never really test their capacity for hard work. Spending more time in the squat rack will lead to bigger lifts and improved development for anyone.