Lots of light, good air circulation, no extra nitrogen, and no overhead watering are the best cultural practices to help avoid late blight on tomatoes.
You should find out which copper products are registered in your state for late blight. Copper is acceptable for use on commercial organic farms, but it's not considered very effective, and works only as a preventive measure. You have to apply it on every leaf surface (including the undersides) for it to work at all. It won't help if disease has already hit your plants, and it washes off with every rain.
Plant breeders have developed several late-blight resistant varieties of tomatoes in recent years. I grow Defiant, Mountain Magic, and (this year) Plum Regal--resistant varieties, but I haven't had an outbreak in my garden in the four years I've been growing them. I had Juliet, another somewhat-resistant variety, the year we got struck hard. Juliet didn't resist that outbreak. It got infected as early as the other varieties. We lost all 75 plants before harvesting a single fruit.