Something I've come to believe in recent times is that average person beginning training would be best served only training 1 - 2 x per week.
And even if you're not a beginner, understanding how to make such a low training frequency work is a tool that will definitely come in handy at some point in life.
'Optimal' vs. Reality
To be clear, training once per week is not optimal for most people. Research and decades of anecdotal evidence would indicate that somewhere between 3 - 5 days is likely the sweet spot.
However, human aren't robots. If you are currently doing zero training sessions, then expecting yourself to be able to begin consistently following a 5 day training plan is unlikely to work for long. Even amongst regular gym-goers, almost none of them can keep 3 days a week going for the entire year.
So maybe you should ask yourself: what's the minimum amount of days that I could do every week, regardless of work stress, family commitments, etc? If you look deep inside, you'll probably find it's a lot less then what you'd like. And if you're brand new to training and have no mental habits formed, one day per week may be the most realistic option.
Making a Low Frequency Plan Work
Beginners can usually progress on one day, as long as their sleep and nutrition isn't complete rubbish. More experienced lifters will mainly use this plan as a method to maintain gains during busy/stressful periods of the year.
The key to making one day per week work is:
1. Keep it Simple
Just aim to get the meet and potatoes of a strength programme done. I advocate one exercise for each major movement pattern. This means one squat, hinge, push, and pull movement. This could be squat, bench, deadlift, and pull-up. Get the important stuff done and get out in under an hour.
2. Pick the Right Day
Make sure you pick a day that has the fewest obstacles. Sunday for example is usually a terrible choice for most people, because it's highly likely you'll be hungover at some point. Monday, on the other hand, is when most people are highest in motivation. Just be realistic about your schedule and what's likely to crop up.
3. Focus on Recovery
You can get more out of 1 - 2 days than you think if you eat and sleep properly outside the gym. I will always take two days per week with solid recovery over 5 days a week of eating and sleeping like crap.
Training once per week shouldn't be a permanent thing. If you're newer to training, use it as a way to succeed every week and build habits. If you're more experienced, use it to maintain your gains when you can't feasibly make it to the gym multiple times per week.