As women, we often say "yes" when we really would like to say "no." That's where good boundaries come in. Just as property ownership requires good boundaries to mark where your land begins and your neighbor's ends, so too in our relationships, we need good boundaries.
Perhaps you've experienced someone stepping over a line for you—or you've said "yes" way too many times and are now angry and resentful. Boundaries are a cure for that.
It's not always easy to learn to set boundaries if you've been used to doing whatever others want and disregarding your own wants and needs. But it's never too late. First, you need to determine what you want and need. Second, you need to (gently) let others know. I say "gently" because boundaries aren't about punishing others. They're simply like fences to let others know how far they may go.
Say you don't want to serve on the hospitality committee any longer. You've done it for years. It really is okay to say, "It's time for me to step away from this." You don't need to offer an explanation—unless you wish to do so. But saying "no" doesn't require it. Or say you don't like when a friend always assumes you're going to drive when you go places with her. You get to say "no" to that. It's okay to suggest that you take turns.
Perhaps someone speaks to you in a way you don't like. You get to say that it's not acceptable.
Finally, you determine consequences if the behavior persists. It's okay to say that if this behavior persists, you'll walk away when the negativity occurs. If it doesn't stop at all, you get to decide whether you need to even walk away from the relationship. You're the only one who can decide where to erect your fences or boundaries and what will happen when they're breached. Again, this isn't about punishment. It's simply about maintaining your boundaries and staying healthy.