Crabgrass is a common weed that can be difficult to control once it has taken hold in a lawn or garden. The best way to prevent crabgrass is to take steps to keep it from germinating in the first place. Here are some best practices for preventing crabgrass:

1. Maintain a healthy lawn: A healthy lawn will be better able to compete with weeds like crabgrass. Make sure your lawn is properly fertilized, watered, and mowed at the appropriate height for your grass type.
2. Use a pre-emergent herbicide: A pre-emergent herbicide is designed to prevent weed seeds from germinating. Apply a pre-emergent herbicide in the spring before crabgrass seeds have a chance to germinate.
3. Reduce soil compaction: Compacted soil makes it harder for grass to grow and easier for weeds like crabgrass to take hold. Aerate your lawn in the fall to reduce soil compaction and promote healthy grass growth.
4. Don't overwater: Crabgrass thrives in moist soil, so be careful not to overwater your lawn. Water deeply but infrequently to encourage deep root growth in your grass.
5. Keep your lawn well-maintained: Regularly remove any weeds that do sprout up in your lawn, and avoid leaving bare patches of soil exposed. Crabgrass and other weeds are more likely to take hold in areas where there is no competition from grass.