You basically want high fiber and avoid red meat and tuna.
Poultry and most seafood won't have the heme iron content that red meat has.
Non heme iron is more likely to go unabsorbed in the GI tract and be eliminated through the stool.
High fiber content in the intestines reduces efficiency of absorption of various metals including iron.
While diet certainly can help, regular phlebotomy to remove extra blood is a standard therapy.
Also alcohol is really bad as it can increase the damage to the liver caused by the high iron and you should avoid supplements with iron or vit C in them as ingredients. Naturally occurring vit C is fine in fruits and vegetables, but don't use supplement form of it. Raw fish should be avoided as people can be more prone to infections with hemocromatosis.