The most important thing to understand when training athletes is the difference between G.P.P and S.P.P. Also, it's important to understand that mastery in a specific discipline does not mean mastery in weight training. In fact, it is usually the opposite; master of one thing, beginner of another. This is very lucky for you, whether you are a coach or an athlete. What this means is that you don't need advanced or fancy training methods to achieve results. Besides the huge pile of dung that is "sport specific training", the misunderstanding of training mastery by elite athletes is ruining training.
What is the worst thing you see people doing? Keep it fitness related. Novice lifters listening to novice lifters on message boards – it’s like two Navy recruits running a nuclear submarine. Nothing good can happen.
Now if you're a beginner and are working out without any guidance whatsoever, it's probably best to just stick with the basic program. One of the worst things a young lifter can do is take advice from other beginners on message boards – they usually have all the advice and none of the experience.