How is a diabetic foot ulcer best treated?

Depends on site. This is dependent on many factors: locations, depth, involvement of deeper structures, underlying deformity, present medical status, actual cause (not all ulcers in diabetics are diabetic related) and compliance of the patient.
Multiple remedies. Wound care requires multi-discipline input for proper wound healing. There are multiple modalities and multiple strategies to get a wound closed but it takes a knowledgeable well trained specialist to know when to implement the appropriate treatment during the course of wound healing using evidenced based medicine.
4. 1. Keep weight off the foot. 2. Control diabetes. 3. Don't smoke. 4. See a podiatrist.
Dfu. Cannot answer directly as these need to be seen. A well-trained clinician will take a history, evaluate, consider the factors of the diabetic control, the depth and status of the wound (Wagner Stage), infectious considerations, vascular status (clinical and testing), and then push for redistribution of pressure, ideally with a total contact cast.
Wound care. . Diabetic ulcers will generally heal if you offload the area (decrease direct pressure with an insert, or a wheelchair), have your doctor trim the callus and dead tissue away on a regular basis, and if the ulcer is infected, you may need oral or IV antibiotics, depending on the severity of the infection.
Special care. Offloading of diabetic foot ulcers, good nutrition, glycemic control, regular wound debridement by your physician, and local wound care are essential for wound healing.