Make sure your claim is related to a question of federal law. To file a lawsuit in federal court, the underlying claim must be directly related to an issue protected by the United States constitution, federal law, treaty or federal act.
Make sure that if your claim is not related to a federal question, that it has diversity of citizenship. Diversity of citizenship means that "no plaintiff can be from the same state as any defendant."
Make sure that if your claim falls under diversity of citizenship, that the amount or value in controversy exceeds $75,000. The damages must exceed this value on their own. In other words, legal fees, interest and expenses cannot be added to the underlying cause of action.
File a copy of your complaint, pay the fee and serve the defendant. Failure to comply with service of process will void your complaint. You might be able to refile, but that is up to the court.
File your complaint in the correct district. Some states have two or three federal districts. To correctly file a lawsuit in federal court, you must file either where the defendant resides or at its principal place of business. You can also file in the district where a substantial portion of the events that gave rise to the action occurred.