How to build receptive understanding in a child?

My child is 3, diagnosed with ASD. He responds to name, makes eye contact with familiar people, can point to request and share. He has some understading for people, nouns and some verbs. He does not understand sentences or complex language or past, future or abstract ideas. He is taking speech therapy (3 times a month) and the progress is slow so I want to work with him at home.

Has anyone gone through this? What helped?