For slugs, it took a long while until we discovered an easy way to repel them. An older gentleman that works with us at the same restaurant as a dishwasher is also the restaurant’s gardener. The looks fabulous year-round! installing a copper rim around your plant beds as wide as an half inch stops snail, slugs and even caterpillars from crossing; tested, successful, so approved and still used by me every time I add a bed.
Secondly, for small insects like spider mites and aphids, you can use soapy water. It can’t be overly soapy but with good suds plus we add different things to it, if we steam veggies we use the water for the mixture the next day just to add some nutrients to the soil. We only apply this as needed if we notice a problem we remedy it immediately.
Also knowing your insects is just as important as knowing your plants.