Model for your child requesting, sharing, or taking turns.
Use praise to encourage these skills.
Label your behaviors. “E.g. while taking turns say “I love taking turns with you when we build a tower.” You can teach your child these skills without being directive and making him feel like this is a therapy session.
It is also important to allow your child to feel like he is leading the play. It will build his confidence in his play and imaginative skills.