Use Cabbage Collar - and row cover - Cabbage worms are the worst pest for brassica plants, so watch out for them on your broccoli plants
Flea beetles can also be a major pest for broccoli seedlings
Broccoli grows best in cool weather, so if you live in a warm climate then you should avoid growing broccoli during the hot summer months
Mulch around the base of the broccoli plants to help keep the roots cool
Broccoli plants like a lot of water, so never allow the soil to dry out completely
Feed your broccoli plants throughout the growing season for best results. You can use the same types of liquid fertilizer you use on the seedlings (e.g.: liquid compost tea, compost tea bags, fish emulsion, liquid kelp)