Several things:

1) most iron supplements are constipating and offer poorly "bioavailable" iron. The best supplement I know is liquid Floradix B-complex with iron. You can buy it from Amazon or Drugstore.com. The bad things about it: 1) you need to store it in the fridge 2) it is expensive 3) you need to take it 1/2 hour before a meal, so you need pre-planning. But it works the fastest, tastes great, and offers the full B-complex to boot.

2) you need to combine iron-rich foods with sources of vitamin C in one meal for better absorption

3) animal sources of iron are better absorbable by the body than plant sources

4) cooking in a cast-iron skillet does add iron to your diet, so it is a great way to go

5) iron foods act synergistically: eating several sources of iron in one meal is the best.

6) for a while, stop eating iron-rich foods with foods rich in Calcium, such as dairy products, in one meal. The presence of calcium-rich foods inhibits the absorption of iron. Separate them.