Hi, we'll have our 4D/3N visit in Hong Kong and planning to have sidetrip in Macau.

Well, here is my general suggestion:
You can spend three days in HK and one day in Macau.
D1: After your checking in your hotel, you can visit the peak, where the peak tower and Madame Tussauds Museum can be enjoyed. After that, Avenue of Stars and China Harbor City are suggested for you. At night, the Symphony of Lights at Victoria Bay is recommended.

D2: Ngong Ping 360/Giant Buddha comes first. Afterwards, the Disneyland Resort can be visited and it deserves a half day. At night, you can go to the Temple Street Night Market.

D3: Ocean Park is a must for your HK trip. Then you can go for shopping at Causeway Bay area. If you are interested, at night, the pubs and bars in Lan Kwai Fong should not be missed.

D4: In the early morning, take a ferry to Macau, where the Fisherman Wharf, Venetian Resort, Senado Square, Ruins od St. Paul and Macau Tower can be visited. You may leave from HK. If so, take a ferry in the afternoon back to HKIA to take your plane.