How to measure public opinion for politics.

You are a political consultant for a campaign for public office. The campaign manager is looking for your advice on how to measure public opinion, and how to persuade the public that they should vote for your candidate.  What are some things that that you should be wary of when attempting to measure public opinion?  What are some things that the campaign can do to change peoples minds?  What are some features of the origin of public opinion about which the campaign cannot do anything?  What role might the media play?

Hopefully this helps.