Preparing the containers for sprouting further the tomato seeds...
Here, I use regular indoor/outdoor vegetable soil medium you can buy at the garden center... "seedling starter soil", I have found is not as good. Again, I use previously boiled water that has been cooled... reason being, the salts in the water seem to dissipate and not be so problematic to the seedlings. Make sure the soil is mixed with the room temperature boiled water until the soil is quite damp but not running, like at a clumping stage.
I recycle washed milk gallons to plant the seeds in, as I have found them to be the best as they act as a little greenhouse and protect the seedlings from the cold on your window sills. Tomatoes love the room between seeds and the deep 2 inch soil I give them initially.