I used to be a terrible people pleaser.
I was desperate for people to like me and was a complete doormat.
What helped me was thinking things through and telling myself that I am as important as anyone else and I don't have to put my needs to one side at al times. It's OK to put myself first sometimes.
Prepare yourself. So when someone asks you to do something, your instinct is to blurt out yes.
Instead, train yourself to say I'm not sure if im going to be able to do that, I'll get back to you.
Give yourself some time to think.
Ask yourself "and then what happens"
So and so will be mad at me
Ok. And then what happens?
They'll not talk to me / shout at me / put a passive aggressive post on FB.
Ok. And then what happens?
Unless you're dealing with people that will cave your head in if you don't do what they want then what is actually going to happen if you don't prioritise them? And why can't you deal with that? These are things you need to ask yourself.
Also, people pleasers often have people in their lives that they'll happily chuck under a bus in order to please unreasonable people.
It's normally their partner or their children.
Which leads me to the next question. If someone can pick and choose who to please and who to upset then they are a selective people pleaser and absolutely can deal with conflict because they deal with it every time they let their partner down or every time they don't stand up for their kids.
Think about what it is you're afraid of any why you're afraid of it. What it is you think is going to be done to you and why that is something you believe you can't deal with.