Yoga, as commonly taught, in a multitude of versions descended from the Indian tradition, gets some crucial things right. At the same time, it gets some other things terribly wrong.
One obvious thing it gets wrong is attaching metaphysical or religious meaning to all the teachings. But annoying as it can be, I do not consider it a deal breaker for anyone who has half-decent epistemic habits. It is fairly trivial to filter out the wordy noise and benefit from generations upon generations of accumulated and slowly refined practical knowledge.
At it's best, yoga functions as a sort of a operation manual for the human body. If used correctly, it can produce amazing results, often life-changing after some years of practice. This is not so much a testament of the amazingness of yoga itself, but rather of how much we tend to underutilize and mistreat our bodies. The human body, when operating on it's own terms in good conditions, is actually freaking awesome, though it's something hard to explain verbally to anyone who hasn't felt it by themselves.
Unfortunately, yoga comes with a big package of stuff that is not only unrelated to what I'm praising above, but actively working against it. One thing I'd like to single out is the "competitive" mindset that comes deeply embedded in the yoga culture. People who happened to have a great teacher might have avoided the worst of this blow -- but definitely not all of it, and definitely the lucky ones are in a minority.
The "competitive" mindset is present not just in the atmosphere of presumption that surrounds yoga gurus, but even in innocent-looking implicit framings such as having canons of named poses, that specify exactly what it means to do each pose "correctly".
Now in a way, this approach is defensible as a way to make the intangible praxis tangible and transferable between generations. I agree. However, this stated purpose has nothing to do with how beginners should be taught, and setting up a situation in which they aspire to those particular poses, I consider not only counterproductive but harmful and evil. All the "official" poses were originally created and optimized by following natural incentive gradients that lead to maintaining one's body well. These gradients are fueled by time, attention and care, and definitely not competitiveness or setting goals.
If you are teaching some beginners yoga, the thing you want them to grasp the most of all is the sensation and pleasure of doing whatever one's body "wants". This also means being able to pay attention and sense exactly what that thing is. It takes a long practice to ride such weak gradients all the way up to advanced poses and intense exercise. In fact, a group of beginners coming directly from their stressful jobs, unhealthy diets, bad sleep habits etc., might well find that what their body wants the most at the time is to take a nap. And there is nothing wrong with it. In this case, I would advise them to sleep without feeling guilty at all -- it might well be that in their situation, relaxing and taking a nap has the best effect on their overall health among all actions available to them.
In the long term, there is nothing to be gained from making people do yoga poses that they didn't by themselves arrive at feeling that they want to do. This might include copying long sequences from someone more experienced, and thus acquiring some of their knowledge by mimicry. But at no point should this involve pressure to do the poses "well" or "correctly". If one person feels energetic, curious, and wanting to follow someone else's poses or sequences, great. Let them do it! They will learn a lot, enjoy themselves, and not get hurt in the process.
On the other hand, if a beginner believes that the only path forward is to do exactly what the teachers or gurus say, and blindly execute the techniques, ... Well, if they stick around long enough, they might eventually learn to feel and listen to their body and start enjoying the moment-to-moment experience of practice. But they are more likely to quit than get to this point, and even if they get there, they will have accumulated significant psychological debt after so many years of basically forcing themselves to do something they don't really like.
As much as I don't consider myself an expert on all this, I still want to end this rambling post with a concrete recommendation. From a beginner's perspective, it is hard to be selectively critical of a big tradition like yoga, and hopefully what I'm saying is reasonable enough to stand on its own.
So, if you want to start doing yoga in a way that is long-term sustainable, healthy, and above all enjoyable:
Keep offical (guided) instruction well below 50% of your total "yoga time". In fact, 10-20% should be plenty.
Make some time for yourself to freely stretch, relax, and move your body in whichever way feels nice. Play some music. Don't stress about if it looks stupid or not. Don't worry if what you are doing is "yoga" or not. (I call this an "unyoga" session.)
If you don't feel like exercising, just lie on your back and relax. Focus on the sensations in your body and wait. Do you feel like resting? Great, then rest. If you never feel energetic and naturally willing to train, you have bigger problems to solve. Try to improve your lifestyle, and generally give your body more time and attention. If you take care of it, it will respond. Otherwise, there is no point in forcing it to exercise.
Spend time with friends who are physically active, even if what they do is not yoga. Get used to the idea that exercise is fun, and keep it that way.