I am not a trainer, hence I cannot advise youngsters on the use of supplements or the way to build their bodies. But I can tell them one thing that I did - find a good, honest trainer.
I work out every body part twice a week, and that is what helps me stay in shape.
My supplements are similar to my training - I always commit to being a better version of myself.
I learned the ins and outs of the supplements business as a bodybuilder. I'd worked with some of the companies, and I knew a lot about the products. Some of them worked OK, and some of them didn't. I wanted all of them to work, not just for me, but for other people, too.
Time between sets should be short and just long enough so that you are sufficiently recovered to hit the next set hard.
Knowledge is the real power.