Although there are many different ways to approach the legislature to advocate for a particular position, there is one item that is at the core of any approach: always tell the truth. There is only one opportunity to establish credibility so it is never a good idea to exaggerate when talking to legislators. Also, legislators are aware that your version is likely only one of many opinions on any given issue - if you are aware that other opinions exist share them. Not only does this demonstrate that you have a full understanding of the issue at hand it also reiterates that you are being honest and not trying to hide anything.
General Tips for Effective Advocacy
Tips for Navigating the Legislature's Website
How to Testify Before a Legislative Committee
Tips for Building Relationships with Legislators
Tips for Writing Your Legislator