Tip 1: Practice your "No" face in the mirror. You know, the one where you're like "Huh? No, I won't do that." with conviction.
Tip 2: Develop a strong sense of self-worth. You're not a doormat, you're a sentient being with thoughts and feelings.
Tip 3: Surround yourself with people who won't roll their eyes at your "No"s. Find a tribe that understands the importance of being a boundary-setting ninja.
Read Tip 3: Set boundaries like a pro! for more expert advice.