Preschoolers are between the age of three and five. Preschoolers learn through watching their peers and with their peers.
Great strategies to encourage your preschooler to reach their milestones would be to encourage play dates. Make sure that you are there with your child and to model and show your child how to play with their peers using age appropriate toys.
Age appropriate toys and games for a preschooler would include puzzles, games, anything that would involve using maybe tweezers, matching games. Other things would be dolls, trains, dress up play, costumes, a doctor set. Anything that involves make believe play and anything that would involve for them to play a role with their friends.
So either they are dressing up as the part, or they're using their dolls or their trains as the key players. Promoting opportunities for your child to play with their peers as well as reading to your child, playing with your child. Various games, toys and puzzles that are age appropriate will help your preschooler reach their milestones.