This is very important to keep crops healthy. Traditionally, crops are divided into four types:

Legumes
French beans, peas, runner beans, broad beans

Root vegetables
radish, carrot, potato, onion, garlic, beetroot, swede, sweet potato, shallots

Brassicas
spinach, chard, kale, cabbage, cauliflower, broccoli, spinach

Fruit-bearing
tomato, sweetcorn, cucumber, squash, pumpkin, courgette, aubergine

Just make sure you move them around every year with your planting plan, so the same type of crop isn’t in the same place year after year.