Before this can be answered, you must identify the right with which that the person needs assistance. A general list (from least restrictive to more restrictive) includes: 1. making one’s own decisions with assistance from others; 2. various banking options (such as joint checking accounts, direct deposit/payments; etc.); 3. power of attorney and durable power of attorney; 4. representative payee for social security benefits; 5. advanced directive documents (such as living will, or health care surrogate designation); 6. medical proxy; 7. trusts (such as revocable, irrevocable and special needs).
There is an excellent manual on this that is available free of charge titled Lighting the Way to Guardianship and Other Decision Making Options. Here’s a link: http://www.fddc.org/publications/order-online