USCIS recently funded many community-based organizations that help permanent residents prepare and apply for U.S. citizenship. Look at the information at the USCIS website to see where you may be able to get low-cost or free legal services relating to naturalization. In Boston, Massachusetts, the Irish International Immigrant Center is one of the organizations that recently received funding. Also, look at Citizenship Resources to use web resources to learn more about the N-400 Application for Naturalization.
If you have complications (such as criminal convictions, tax issues, or lengthy periods of time outside of the US), you should consult with an immigration attorney about your eligibility for US citizenship. I have helped many LPRs with legal complications win citizenship, and I may be able to help you too.
Please visit Citizenship Resources to use web resources that provide learning materials to help permanent residents prepare for the naturalization process.