An LLC is a very easy entity to maintain. The states have very few requirements for an LLC to remain in good standing. One of these requirements is an Annual Report. An Annual Report is a simple form that you have to fill out every year (or in some states twice a year). Most states charge a nominal fee for the annual report and a so-called "franchise tax" on the company's assets located in that state. Some states always charge a substantial minimal amount for franchise tax (for example, $800 in California).
In addition, your LLC is required to maintain a registered agent
with the state. If you use a commercial company, you have to make sure to pay their fees every year so that they continue to serve as your agent.
Finally, remember to pay your local, state and federal taxes on time.