Identify your key demographic. Your petition will likely hit a certain demographic especially hard, so your summary and background should show evidence as to why action should be taken to benefit this key group. Because the point of a successful petition is to get names, you should also demonstrate how other groups would be affected as well without change.
Grab the reader's attention with a fact, quote, statistic or piece of information that relates to your argument. This is like the lead in a news story, or the abstract in a research paper. It should be concise, but powerful. On a petition, brevity is important. A summary is usually no more than two paragraphs in length. Few people will want to read a lengthy statement; they will simply want a brief summary of why this petition is important.
Provide data that demonstrate the need for action. Do not simply say that a problem exists -- show it to the reader. For example, instead of "unemployment is high," you may include actual percentages that indicate the current unemployment rate. Make sure this number is researched and provable. The administrators of the petition should be knowledgeable enough about the subject to back up claims.
Offer solutions to problems. Using the high unemployment example, your petition might support the need for a high-speed rail to be built in a community that can stimulate job growth and revenue for the state government. Having clear examples of how the changes will improve people's lives will separate your petition from those that just express dissent.
Think of your summary and background as a chance to make a persuasive argument. A persuasive argument should always encourage readers to act in a certain way; in this case, sign a petition. Clearly state why and how an individual's signature will make a difference. You may also want to briefly indicate other actions that could be taken, such as donating funds or volunteering.