Research the rules for declining a bid as established by your school. Some schools require you to decline your bid immediately, so that the sorority can pursue other members; while others give you more time to make a decision. At the University of Virginia, for example, new members have two weeks to decline a bid, and they can attend sorority functions during that period to assess how well they fit in with the sorority.
Return your bid card to your rush leader if you receive your bid on Bid Day. Most sorority members go through traditional rush and receive their bid at the end of that process. If you do not want to accept a sorority's bid, you can indicate that you are declining your bid on the bid card, and your rush leader will funnel the card through the proper channels.
Meet with a current sorority member to decline the bid. If you are going through continuous open recruitment and not rush, you might receive a bid at any time. If you do not want to accept the bid, tell the sorority member who offered it to you that you are choosing to decline the bid. You can continue with the continuous open recruitment process with other sororities.