Everyone is different, so trial and error is the way to go, but some common ones that trigger flareups are: dairy, beef, eggs, definitely citrus, and some kinds of breads, I think it's the yeast, or gluten or just the wholegrain or something.

If you love tomatoes and citrus, just eat small amounts and don't let any of the juice touch your hands or other eczema areas.

I'm sorry you have eczema, it sucks, I have had it all my life, my hands the worst.
Always keep the area moisturised, don't ever let it get all dry and flaky coz that is just so itchy.

Also, wear 100% cotton, and wool is really bad for eczema.