Iron and Zinc compete for absorption. This means that if you're taking an iron and a zinc supplement at the same time each day, they're battling with each other to get across your bowel wall and into your bloodstream. Make their job easier! Take your iron and zinc supplements at opposite ends of the day, so each of them gets a free run.
If you're taking an iron supplement plus a multivitamin, make sure you take the multivitamin at the beginning of the day and the iron supplement at the end of the day, so the iron won't knock the zinc in your multivitamin out of the way. (Why the multivitamin in the morning, and not the other way around? Because your energy levels through the day will benefit from the B vitamin boost in your multivitamin).
By the way, if you've been taking an iron supplement for a while, call into your local naturopath and arrange for your zinc status to be checked (its a simple taste test). Symptoms of low zinc status include slow wound healing, 'toad skin' on the backs of your upper arms, and recurring cold sores or herpes breakouts.
Needless to say, if you've been taking a high dose zinc supplement for a while, check your iron status. Your doctor or naturopath can arrange a blood test for you.