Declaring someone incompetent to handle their own finances is a big step that should never be taken lightly. You will need to prove that the person is incapable of making financial decisions that are in his best interest. The courts will want to see proof that the decisions being made are not the same as a normal, responsible person in the same situation. Just because you do not agree with how someone is handling their finances does not mean you can take over with the court's blessing.
Contact the probate court where the person you want declared incompetent lives. If the person is homeless, contact he probate court in your area and ask who you should go through.
Complete the request for guardianship with the help of a mental health or family lawyer. The lawyer can help you determine the best possible route toward guardianship and help you ensure that all necessary paperwork is turned in to the courts.
Ask the court to order a mental evaluation if the person is uncooperative in obtaining one. When the person is in a hospital getting an evaluation, it is much easier than when they are at home or homeless.
Turn the guardianship application and Statement of Expert Evaluation into the court. Stay in contact with your lawyer after the paperwork has been turned over to the court so you are available to complete any additional paperwork the court requests.
Complete any additional requirements laid out by the judge. Some requirements include submitting to a credit and background check or getting bonded by an insurance company.