Do your research. Imho, the majority of problems are caused by simply not looking into things well enough before getting started. Learn what works for the result you're trying to achieve along with side effects and how to avoid them. Do your blood work! Without bloodwork you are pretty much guaranteed eventual problems. Start slow.... It's a waste of any compound to start insanely high. Your body will react well to even small doses at first. So save the big boy doses for when you are much more experienced. Above all, never stop learning. There is too much info on here to waste it being lazy. Use the search box!
