Halloween is such a magical time for kids. In all that excitement kids can make unsafe or unwise decisions.
As parents, we don't want to ruin the day's magic, but we do want them to be safe. We want them to remember to stay safe when street crossing the street. We want them to respect others' property and be polite, and we want them to stick to areas we are comfortable with.
Because there is so much stimulation happening for children on Halloween, we must practice what we want beforehand. If we want our children to respect others' property, we need to show them what that looks like. For example, if we don't want them walking on the lawn, we need to take them out and physically practice walking up to the door and back on the sidewalk and not cutting across a law. If we want them to be polite and say please and thank you, we need to practice it with them.
Another part of keeping kids safe during Halloween is understanding their individual needs. For some kids, large crowds or "scary" looking houses may present a problem, so showing them how to respond to those situations will be extremely helpful to avoid meltdowns and anxious feelings. 
The more you can prepare your child for what may happen on Halloween and how they need to respond, the better the actual night will go.