How do you increase your ferritin levels?

I got my ferritin level tested while I was also getting my TSH checked, and it (my ferritin level) was at a 16 I think. I know that it helps to have your ferritin levels above 70 or 100 if you want your hair to grow/be healthier, so I was wondering if anyone knew how to raise your ferritin level(s)? any advice/suggestion is welcome:)