There maybe 100s if not 1000s decisions come to you on which you need to say yes or no.
Just imagine if your close friend come right now and ask you to go to party or clubbing, would you accept it or not?
You'll say YES if you are in 90-97% of population. If you're not then congratulations! If you are one of above it's not a skill that you can't master.
Saying no is a skill that you've to master if you want success in your life. Not many people talk about it but it's so much crucial.
What you say in your daily life and decide mold your future. I'm not saying just quit every fun stuff. I'm saying just decide wisely.
Now you maybe thinking how to know whether I'm choosing wisely or not?
I've the answer for this. You just need to ask one question: "Does this decision help me towards my goals or life I want or against?" If yes, go for it. If no, then say NO!!!
This can answer all your doubts. After that it's all upto your willpower to stand still on your decision.