Allow parsley, carrot and celery to remain in the ground over the winter. They will produce flowers the second season and attract beneficial insects. Also, plant strong smelling herbs among vegetable crops. Try some combinations that folklore says are effective companions. Radishes make excellent trap crops for cucumber beetles among squash and cucumbers.
Radishes also attract flea beetles when planted near cole crops.
Garden borders planted with low growing thyme or lavender may deter slugs. Tansy and pennyroyal repel ants. Observe your plantings carefully, and write down combinations that seem to work for pest control and growth enhancement. Communicate your observations with others. Try to replicate your observations or have others try the same combinations.