Smoking: Smoking causes lung diseases that damage your air way and the air sacs found in your lung. This could stop you from participating in activities that require excessive amounts of air, (for example, running, or playing some sports) and would slow you down considerably. So don't smoke. Also, try not to be around anybody that DOES smoke, as you would develop second-hand smoke, and the outcome for second-hand smokes are worse than the ones gotten by the smoker himself/herself.
hope this helps