How can I help my child during his preschool years?

Love, structure. Preschool children need affection and praise when they do well, a structured environment with consistent "rules" such as no hitting etc, regular sleep schedules ( about 10 hours/night), good nutrition of fruits, vegetables, whole grains, lean protein, and dairy. Avoid sweetened drinks. They need time to run around and play and intellectual stimulation reading books and interacting with you!
Many Things. Be positive be supportive supervise challenge their senses in play socialize with other kids as a start!