how do you stop being a people pleaser?

i used to struggle with this as well, what I learned to do is always think about how you'll feel after ur actions. Will it benefit u or the person ur trying to please, and would they have done the same / gone through the same things for you? Also just stop caring about what people think abt u cuz most of the time they would never do the same 4 u

dont care about other ppl, epic win

To put it simply; just don't care.
It's not very simple to just not care, it takes a bit, especially for someone who's not used to saying "no" to others. I was like that too a few years ago, still am a tiny bit. 

Anytime someone asks you to do a favor that you wouldn't be pleased to do, make up excuses. Try to not feel bad for them. Half of the people who can't tell if a person is unwilling to do things for them are aholes (in that topic, not entirely overall). Think of yourself as another person you love in that situation. You wouldn't want them to do it just because they feel bad, so why would you? - That's type of mindset made me not feel bad for saying "no".
If the askers are the types to get mad if you say "no" to them, don't do it. It's better to not contribute to their selfishness.

Things that are important to learn:
- saying "no" directly
- saying "no" indirectly (actual excuses, giving reasons why you won't/can't)
- making small lies (it's okay to lie sometimes. If you can't bring yourself to -the first two points-, lie about it. You don't have to be specific about it. You can just say that it's private or family matters.
"My parent needs me home to help them with chores",
"my parents are coming home so I have to go home and clean before they arrive",
"I'm already doing tasks for my cousin",
anything! 

It's better and more convincing to make things up including family or someone that asker doesn't and won't know.
And when you do refuse to do things, it'd be more affective if you were to be in a hurry. Don't stop for them. That'll make them try to convince you more.

No, you won't be a liar, you're just not wasting your own time with their wants that they could simply do themselves. I wish the best for you!