Answer:
When playing the sport one should know their assignment. What are you to do on a certain play and how well you do it. On defense one should read the play not guess, guessing will lead to a big play from the other team (Its ok to guess sometimes but I do not strongly recommend it). When tackling one should sink the hips and tackle low (attack the legs if you wrap someone's legs they dont have anywhere to go. Gang Tackling is highly encouraged not matter what level of football you play. When running the ball if you run into a large group of people you should double cover the ball at both tips with your hands. Also use your blockers when on offense and when on defense use a swim or rip move to get by blockers to make the tackle.
(If you do not understand a term I used you should youtube it. They give you a visual on how it is suppose to look)