Gather supporting evidence, including records that support the claim that your spouse is incompetent to make decisions on his own, handle finances, or direct his own medical care. This can also include statements or affidavits from physicians, caregivers, relatives, friends, acquaintances, colleagues -- anyone who has contact with your incapacitated spouse. Contact any witnesses who can support your claim of guardianship and request their live testimony at the trial or hearing that will take place.
File a petition for guardianship in the court having jurisdiction over your household. In most cases this will be a state, circuit or county court. Submit your gathered evidence and include in the petition your grounds for requesting legal guardianship. If state law requires it, add a certificate of service that serves as your sworn statement that the petition has been furnished to your spouse and any interested parties, including relatives you list on the petition. Sign and date the petition as well as the certificate of service.
Schedule a court trial with the clerk if the guardianship petition is contested, either by your spouse or by another concerned party, such as a parent or other close relative of your spouse. Schedule a simpler and shorter court hearing if the petition is uncontested. Bring your evidence and witnesses to the hearing and respond to any questions asked by the presiding judge or magistrate. The judge will either grant your petition and appoint you as legal guardian or deny it, either "without prejudice," meaning you can amend or correct it; or "with prejudice," meaning the case is closed and you will have to open another one by filing a new petition.