Ferritin level is very low at 14. Gonna start taking iron glycinate. Better with or without food? Any Foods or supplements to avoid when taking it?

Your choice. I am glad you are being treated for iron deficiency. Be sure you know why it happened. It may be monthly loss, a bleeding ulcer or cancer, ill-advised vegetarianism, hookworm, or any of many others.
With food. Taking iron with food will lessen the likelihood of stomach irritation.Wish you good health! - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form.
Practice safe sex, if you have sex.