If a soil test shows the pH is below 6.0, apply lime. Wide spacing assures good air circulation, which discourages diseases. Plant seedlings in the ground deeper than they were growing in their pots so the lowest leaves are just above the soil level. Roots will grow along the length of the buried stem, resulting in stronger plants. And, don't forget to water freshly planted seedlings.
Most experts recommend fertilizing at planting time.
But go easy on the fertilizer. In this case, less is best because too much nitrogen fertilizer results in vigorous vines with few tomatoes. This keeps vines and tomatoes off the ground so the fruits will be larger, cleaner and less apt to rot. Supported plants are also easier to care for and tomatoes are easier to harvest. Many ingenious systems for supporting plants have been devised.