Cleanliness is the most important part of pest prevention. Keeping the grow room clean will eliminate potential habitats for pests and kill germs and spores.
If you grow a group of plants from clone (or seed) to harvest at the same time, pest prevention can be as simple as thoroughly cleaning the entire grow room between harvests. During growth, just make sure to pick up any leaves that happen to drop off and wipe down the walls, floor, ceiling and containers every week or two. Make sure your ventilation is set up properly.
If you grow your plants with a rotational schedule (i.e. if you have 3 flowering plants at all times and harvest one every three weeks, replacing the harvested plant with a new plant ready to flower) it is much more difficult to thoroughly clean the grow room. For proper pest prevention, I recommend removing all the plants at least once a month to clean the grow room.
It is also important to wear clean clothes and shoes and wash your hands before entering the grow room, so you don’t introduce any pests yourself. A 10% bleach solution is great for cleaning a grow room that is free from plants. Soapy water will work well for a plant-occupied grow room. Never use any pesticides on your marijuana plants.