Always plant tomatoes deep, and on their sides.

Dig out a shallow trench. Remove the lower stems and branches off the tomatoes, leaving only the upper most top leaves.

Planting tomatoes on their sides allows the entire stem that is buries to form roots, giving the plant the best foundation possible and allowing the plant greater ability to absorb nutrients and water. Plus a larger root system near the soil surface will meant that more heat will be available to the plant, producing earlier tomatoes. 
I built this little hoop house over my newly planted tomatoes to protect them from frost if we happen to have any in the next week or two. It should warm up the soil a bit too to speed up fruiting.

I built this little hoop house over my newly planted tomatoes to protect them from frost if we happen to have any in the next week or two. It should warm up the soil a bit too to speed up fruiting.