If you have spent a few years as a permanent resident of the United States, then it's likely you can file for U.S. citizenship soon, and fairly easily (barring any complications like a criminal conviction). The cost is relatively low and the benefits are great, as you will see below.
The top ten advantages to being a U.S. citizen as compared to being a permanent resident are:
1. No need to renew your green card. As a United States citizen, you will not need to renew the card proving your status as a lawful permanent resident every ten years. What's more, you will no longer be required to carry your green card or proof of status with you on an everyday basis (although you will need a federal U.S. ID or passport when traveling).
2. Reduced risk of removal (deportation). Green card holders can be removed for committing certain crimes or doing other acts that match the grounds of deportability found in U.S. immigration law. A U.S. citizen cannot be deported. However, be aware that U.S. citizenship may be taken away from you if USCIS finds that you lied to obtain either lawful permanent residence or your U.S. citizenship.
3. Easier travel and reentry into the United States. You will no longer have to deal with the lines of green card holders awaiting entry at U.S. airports, borders, or other entry points. U.S. citizens enter separate lines, and the scrutiny is much less. In addition, as a U.S. citizen you often enjoy easy entry into other countries around the world. In many instances, you can visit foreign countries without a visa.
4. No loss of status after long trips outside the United States. If you spend months or even years outside of the United States, you will not, as a U.S. citizen, risk losing your right to return. By contrast, a permanent resident who leaves the United States for more than 180 days can lose the right to the green card upon reentry into the United States. The immigration officer can deem the person to have abandoned the green card. (If you currently know you will be leaving the United States for more than six months, speak to an immigration attorney. You might be able to obtain a reentry permit prior to leaving.)
5. Ability to petition for more family members to immigration. U.S. citizens can petition more types of family members into the United States than green card holders. Only U.S. citizens may petition parents, siblings, and married children. In addition, in the cases where both U.S. citizens and green card holders can do a petition (such as for spouses), the wait time tends to significantly shorter for U.S. citizens' relations (with exceptions; consult an attorney for details).
6. Ability to pass U.S. citizenship to children who have green cards. When you become a U.S. citizen, your unmarried children under 18 will automatically become U.S. citizens, too. However, they must be lawful permanent residents; must be residing in the United States; and must be in the legal and physical custody of the naturalizing parent.
7. Ability to vote and run for public office. Only United States citizens may vote. Naturalized U.S. citizens can run for most (but not all) elected public offices.
8. Ability to obtain government jobs, grants, other benefits. Certain government jobs require U.S. citizenship. These include many local, state, and federal government positions. Many federal grants and scholarships are available only to U.S. citizens.
9. Tax and estate planning benefits. United States citizens and permanent residents are not always treated in the same way for tax and estate purposes. Speak to a Certified Public Accountant about these issues.
10. Ability to obtain a U.S. passport. U.S. citizens have the right to obtain a passport and the ability to obtain assistance from U.S. embassies and consulates when traveling in other countries.
If you meet the legal requirements, and don't have any complications, becoming a U.S. citizen is a fairly straightforward process. You start by filing the N-400 application and paying the application fee (or requesting a fee waiver).
While you wait, you'll need to study for the civics/government test, and work on your English language reading, writing, and speaking skills.
You'll eventually (possibly after months) be scheduled an appointment at an application support center (ASC) for fingerprinting and a background check (biometrics). Then some weeks or months after that, you'll interview with a USCIS official and take the English and civics tests. Hopefully you will be approved for naturalized citizenship at that interview.
The final step is the oath ceremony where you will receive your certificate of naturalization and be able to enjoy the benefits described above.