Need to learn to stand up for myself

I try to avoid conflict as much as possible. I hate making people upset. So I often end up going along with things just because I don't want to make a fuss.

I know I should stand up for myself sometimes, but it seems like more trouble than it's worth. It's been getting me into a lot of shitty situations lately, but building up the confidence to speak out is really hard for me.

Any advice for someone like me?