If a bill deals with a problem you admit exists, but you believe the bill is the wrong approach, explain what you believe is the right approach. You do not need a crowd to lobby. One, or possibley two, well-informed lobbyists on the same subject are more effective and less confusing than a large group gathered at the same time. When you introduce yourself, save time by making it clear who you are and what organization, if any you are working with. If you are cooperating with some group from the legislator's home district, mention it, and the fact that the home district group may also be trying to reach the legislator.
Most legislators have many demands on their time.
An elaborate sales job or long emotional speech will not be appreciated. They do however, want your well-prepared facts and views, presented in a straightforward manner. Make sure their time is well spent in talking to you. It is easy, particularly when dealing with legislators who disagree with you, to become angry and grustrated. If you disagree, a calm, reasonable attitute and a set of well-prepared reasons for your position may change their minds on the issue.