If your business is owed money by an LLC, the LLC is a separate entity from the owner or manager, and you'll need to sue the LLC, not the individual. It's wise to hire an attorney who can competently represent your interests, particularly if there is a large sum of money in dispute. But you can file the initial pleadings yourself if you want to get the suit filed as quickly as possible.
Determine the legal name of the LLC. Some businesses do business under a different name from their registered name. Visit the website of the secretary of state or division of corporations in your state, then look for the company according to its owner or the name under which it's doing business. You'll have to sue the LLC under its legal name.
Visit the clerk of court in the county in which the LLC does business. Ask for a blank civil complaint form. Many counties offer complaint forms specific to certain issues; you might be able to get a landlord-tenant lawsuit or a complaint for breach of contract. In some counties, however, clerks don't offer blank forms, and you'll have to draft your own. Outline the specific issues within the case, sticking only to legal issues; complaints should be relatively short.
File the suit in the county in which the LLC does business by giving a copy to the clerk and asking her to file it. You will probably have to pay a filing fee. Then have your landlord served with a copy of the suit. In many states, the sheriff can serve the defendant for you for a fee, but some states require you to use your own process server. Ask the clerk if the sheriff can serve the defendant. If this is not an option, you'll need to submit proof to the court that the LLC was served.
Gather your evidence and witnesses. You'll have to present this information at trial. The LLC will be required to file an answer and appear at all hearings. If it does not file anything, you can file a motion for default judgment. This motion is a request to win based on the fact that a party to the suit has not filed a response and is therefore not objecting to or defending the suit.
If you are a sole proprietor and your business is not incorporated, you can usually sue in small-claims court if your lawsuit is only a few thousand dollars.
Owners and proprietors of LLCs aren't liable for their business's actions in most cases. If you sue the LLC, and it goes bankrupt, you might not be able to get any money.