Understand what is required of you in order to achieve your goals.
I was recently speaking to someone who told me he wanted to get stronger. When I asked him what his training was like, he told me he was following a popular program he found on the Internet that had him doing 25 rep sets on his key lifts. He then questioned me as to why I trained my key lifts in sets of 1-5 reps.
Here is a person who at least knew exactly what he wanted from his training but had absolutely no understanding of how to achieve it. He was lazy and didn't bother to do any kind of basic research, so just jumped on to the first program he saw that would fit in to his schedule and promised him the results he wanted. He has just wasted the last 6 months he spent in the gym.