Plant on raised beds. Raised beds improve drainage. They also warm up faster than level soil which aids in faster emergence. Slow emergence increases chances of seedling disease. Use proper plant spacing.
Crowded plants reduce air circulation which enhances leaf spot diseases.
Septoria leaf spot on tomato is an example. However, in Far West Texas, with low humidity and few leaf spot diseases, crowding tomato plants may reduce losses to curly top virus by shading the plants and making them less attractive to the insect vector. Overplanting where possible will ensure enough production if some plants or fruit are lost to disease. Plants receiving all needed nutrients may resist some of the less vigorous disease- causing organisms. Do not overwater.