You can't. Chemotherapy has risks and side effects like all medicine. You can decrease some risks by eating a healthy diet, getting good sleep, drinking lots of fluids, and staying in good communication with your doctor. Accupuncture, massage and naturopathic care can help. The risk of not getting chemotherapy is higher than the risk associated with chemotherapy if your doctor thinks you need it.
Depends. 1) do you "need" cytotoxic chemotherapy? For some cancers we can estimate the benefit (= absolute risk reduction). The benefit is not worth it to some people. 2) on chemo you can watch for signs of side effects to treat them quickly. The role of chemo, dosing, & hazards are highly individualized. If it was easy you wouldn't need specialists to counsel decision making on treatment decisions.