Something that can be damaging to progress, like any pseudo-science is “commonly known” incorrect knowledge. Here are a couple to think about.
To Lose Fat You Do Lighter Weight and Higher Reps
Incorrect. The most effective way to burn calories and raise your metabolism for the rest of the day is to lift as if your aim was to build muscle. With maximum effort, failing around 10 reps or so. You need to ensure you are activating the correct muscle fibres, which lightweights will not be recruiting.
If Women Lift Heavy They Will Get Masculine
Incorrect. Women just simply do not have the hormones to build bulky masculine muscle. The image most people conjure in their head of what they will look like is usually a female bodybuilder with significant steroid use. Naturally, the heavier and more effectively a woman lifts, the more toned and shapely they will become.
Toning Is a Muscular Function
Incorrect. A muscle gets bigger or smaller. It does not change shape or tone. To have a muscle appear “toned” you need to develop the muscle (make it bigger) and reduce the layer of fat covering it, which conveniently are achieved by training in exactly the same way, as above!