While it's nice to be invited to weddings and birthday parties, sometimes you have to say no. Maybe you've made other plans, the destination is too far or you just don't want to go. Whatever your reason, there are a few steps you can take to ensure the would-be host won't be offended when you politely decline the invitation.
Send it in. If you've received a written invitation, like to a wedding, declining politely is easy. All you've got to do is fill out the RSVP card. You may only have to check a box. Since we live in an increasingly digital age, e-vites have begun to take the place of written invitations. If you're declining an e-vite, simply choose the proper response and hit send. No explanation needed.
Ask for time to think. A face-to-face invitation can be tricky, especially when you know you're going to have to say no. The polite way to handle this situation is to ask for time to check your calendar. Then, rather than saying yes to the host's face and backing out later (making you look like a flake), you have time to craft a proper, polite response. Just make sure that if you've been invited in person that you decline in person. It's the polite thing to do.
Be gracious. Even if you have to decline the invitation, express your gratitude to the host whether or not you're going to the event. Thank her for the invitation. After all, you made the invite list when others may have been left off. When you decline the invitation, stay positive. If your only reason for declining is a conflicting event, offer up to the host that you would've definitely come if the dates had been different.
Be honest. This may be the most important step in politely declining an invitation. You wouldn't want people to lie to you, so it's common courtesy to provide an honest reason you can't attend the event. You don't have to be blunt --- don't hurt the host's feelings --- but lying isn't polite. Just consider your reason for declining and come up with a polite way to say it. The host will appreciate your honesty.